I'm after a mains powered battery charger that will maintain a 12v
lead-acid bettery at or near the ideal 'float' voltage while the
battery is in use.
All the chargers I have, including a recently bought one that sounded
as if it work don't do what I need. They charge the battery fully (up
to 14.4v or so) then drop back to a trickle charge which doesn't
maintain the battery at 13.5v or so. I have to restart the battery
charger each time I see the voltage has dropped down towards (or
below) 12v.
All these chargers would be good for keeping a disconnected battery in
good condition but are useless for maintaining a bettery in use.
Chargers that run from solar panels mostly do what I want (I have one
on my boat which works very well) so it's definitely possible to have
a charger that works like this.
So, has anyone any ideas how I can specify what I want? I.e. some
magic keyword that might work?
Chris Green <cl@isbd.net> wrote:
I'm after a mains powered battery charger that will maintain a 12v lead-acid bettery at or near the ideal 'float' voltage while the
battery is in use.
All the chargers I have, including a recently bought one that sounded
as if it work don't do what I need. They charge the battery fully (up
to 14.4v or so) then drop back to a trickle charge which doesn't
maintain the battery at 13.5v or so. I have to restart the battery
charger each time I see the voltage has dropped down towards (or
below) 12v.
All these chargers would be good for keeping a disconnected battery in
good condition but are useless for maintaining a bettery in use.
Chargers that run from solar panels mostly do what I want (I have one
on my boat which works very well) so it's definitely possible to have
a charger that works like this.
So, has anyone any ideas how I can specify what I want? I.e. some
magic keyword that might work?
A Smart Charger designed for caravan / motorhome leisure batteries should
do the job.
Brian <noinv@lid.org> wrote:
Chris Green <cl@isbd.net> wrote:Yes, but how do I find one? I.e. what keywords in my search will
I'm after a mains powered battery charger that will maintain a 12v
lead-acid bettery at or near the ideal 'float' voltage while the
battery is in use.
All the chargers I have, including a recently bought one that sounded
as if it work don't do what I need. They charge the battery fully (up
to 14.4v or so) then drop back to a trickle charge which doesn't
maintain the battery at 13.5v or so. I have to restart the battery
charger each time I see the voltage has dropped down towards (or
below) 12v.
All these chargers would be good for keeping a disconnected battery in
good condition but are useless for maintaining a bettery in use.
Chargers that run from solar panels mostly do what I want (I have one
on my boat which works very well) so it's definitely possible to have
a charger that works like this.
So, has anyone any ideas how I can specify what I want? I.e. some
magic keyword that might work?
A Smart Charger designed for caravan / motorhome leisure batteries should
do the job.
produce hits for just this sort of charger?
On 02/01/2026 09:11, Chris Green wrote:
Brian <noinv@lid.org> wrote:
Chris Green <cl@isbd.net> wrote:Yes, but how do I find one? I.e. what keywords in my search will
I'm after a mains powered battery charger that will maintain a 12v
lead-acid bettery at or near the ideal 'float' voltage while the
battery is in use.
All the chargers I have, including a recently bought one that sounded
as if it work don't do what I need. They charge the battery fully (up >>> to 14.4v or so) then drop back to a trickle charge which doesn't
maintain the battery at 13.5v or so. I have to restart the battery
charger each time I see the voltage has dropped down towards (or
below) 12v.
All these chargers would be good for keeping a disconnected battery in >>> good condition but are useless for maintaining a bettery in use.
Chargers that run from solar panels mostly do what I want (I have one
on my boat which works very well) so it's definitely possible to have
a charger that works like this.
So, has anyone any ideas how I can specify what I want? I.e. some
magic keyword that might work?
A Smart Charger designed for caravan / motorhome leisure batteries should >> do the job.
produce hits for just this sort of charger?
Leisure battery smart charger lead acid
Those should help.
Popular makes are CBE and Sargent.
A Sargent PX300 was very popular on a number of UK built motorhomes and, while it will cope with Lithium, many people upgrade. You may find a
second hand one.
Likewise, the some older CBE ones, while they will charge a Lithium,
people often upgrade to one specified for it.
Victron is a very good make but pricey.
On 02/01/2026 09:11, Chris Green wrote:
Brian <noinv@lid.org> wrote:
Chris Green <cl@isbd.net> wrote:Yes, but how do I find one? I.e. what keywords in my search will
I'm after a mains powered battery charger that will maintain a 12v
lead-acid bettery at or near the ideal 'float' voltage while the
battery is in use.
All the chargers I have, including a recently bought one that sounded
as if it work don't do what I need. They charge the battery fully (up >>>> to 14.4v or so) then drop back to a trickle charge which doesn't
maintain the battery at 13.5v or so. I have to restart the battery
charger each time I see the voltage has dropped down towards (or
below) 12v.
All these chargers would be good for keeping a disconnected battery in >>>> good condition but are useless for maintaining a bettery in use.
Chargers that run from solar panels mostly do what I want (I have one
on my boat which works very well) so it's definitely possible to have
a charger that works like this.
So, has anyone any ideas how I can specify what I want? I.e. some
magic keyword that might work?
A Smart Charger designed for caravan / motorhome leisure batteries should >>> do the job.
produce hits for just this sort of charger?
Leisure battery smart charger lead acid
Those should help.
Popular makes are CBE and Sargent.
A Sargent PX300 was very popular on a number of UK built motorhomes and, while it will cope with Lithium, many people upgrade. You may find a
second hand one.
Brian <inv@lid.com> wrote:
On 02/01/2026 09:11, Chris Green wrote:On eBay that brought up one result that was specifically **not** for lead-acid batteries! :-) I've been trying searches with similar words
Brian <noinv@lid.org> wrote:
Chris Green <cl@isbd.net> wrote:Yes, but how do I find one? I.e. what keywords in my search will
I'm after a mains powered battery charger that will maintain a 12v
lead-acid bettery at or near the ideal 'float' voltage while the
battery is in use.
All the chargers I have, including a recently bought one that sounded >>>>> as if it work don't do what I need. They charge the battery fully (up >>>>> to 14.4v or so) then drop back to a trickle charge which doesn't
maintain the battery at 13.5v or so. I have to restart the battery
charger each time I see the voltage has dropped down towards (or
below) 12v.
All these chargers would be good for keeping a disconnected battery in >>>>> good condition but are useless for maintaining a bettery in use.
Chargers that run from solar panels mostly do what I want (I have one >>>>> on my boat which works very well) so it's definitely possible to have >>>>> a charger that works like this.
So, has anyone any ideas how I can specify what I want? I.e. some
magic keyword that might work?
A Smart Charger designed for caravan / motorhome leisure batteries should >>>> do the job.
produce hits for just this sort of charger?
Leisure battery smart charger lead acid
for quite a while with not much success.
Those should help.
Popular makes are CBE and Sargent.
A Sargent PX300 was very popular on a number of UK built motorhomes and,
while it will cope with Lithium, many people upgrade. You may find a
second hand one.
Likewise, the some older CBE ones, while they will charge a Lithium,
people often upgrade to one specified for it.
On 2 Jan 2026 at 15:13:21 GMT, Brian wrote:
On 02/01/2026 09:11, Chris Green wrote:
Brian <noinv@lid.org> wrote:
Chris Green <cl@isbd.net> wrote:Yes, but how do I find one? I.e. what keywords in my search will
I'm after a mains powered battery charger that will maintain a 12v
lead-acid bettery at or near the ideal 'float' voltage while the
battery is in use.
All the chargers I have, including a recently bought one that sounded >>>>> as if it work don't do what I need. They charge the battery fully (up >>>>> to 14.4v or so) then drop back to a trickle charge which doesn't
maintain the battery at 13.5v or so. I have to restart the battery
charger each time I see the voltage has dropped down towards (or
below) 12v.
All these chargers would be good for keeping a disconnected battery in >>>>> good condition but are useless for maintaining a bettery in use.
Chargers that run from solar panels mostly do what I want (I have one >>>>> on my boat which works very well) so it's definitely possible to have >>>>> a charger that works like this.
So, has anyone any ideas how I can specify what I want? I.e. some
magic keyword that might work?
A Smart Charger designed for caravan / motorhome leisure batteries should >>>> do the job.
produce hits for just this sort of charger?
Leisure battery smart charger lead acid
Those should help.
Popular makes are CBE and Sargent.
A Sargent PX300 was very popular on a number of UK built motorhomes and,
while it will cope with Lithium, many people upgrade. You may find a
second hand one.
I'm not sure that one will do what the OP's after. At least, in the case of the later PX310, the manual states:
--
Once the charging cycle is complete, the charger will remain in the Float Mode
untill the mains supply is removed and re-connected or the power switch is cycled off then on again.
--
IIUC the OP is after something that'll provide above-float charging while the battery's in use. It's something I looked for in the past but couldn't find. And as the OP points out, it's exactly what a solar inverter/charger does.
I'd suggest asking the manufacturer - they're UK based.
IIUC the OP is after something that'll provide above-float charging while the
battery's in use. It's something I looked for in the past but couldn't find.
And as the OP points out, it's exactly what a solar inverter/charger does.
I'd suggest asking the manufacturer - they're UK based.
He seems to want exactly what happens when a motorhome etc is used on rCyhook uprCO ( parked and connected to the mains).
Chargers on motorhomes etc are, essentially, fit and forget- or designed to be. True they have displays etc on the control panels but most owners have little idea what is going on.
I thus need a charger which
will keep the battery charged while it's powering the various devices.
The total drain is probably only about 3 amps so I don't need anything
as powerful as most boat/motorhome installations would expect.
Brian <noinv@lid.org> wrote:
Yes, (OP here) I do. It's actually for a 'UPS' at home to keep the
IIUC the OP is after something that'll provide above-float charging while the
battery's in use. It's something I looked for in the past but couldn't find.
And as the OP points out, it's exactly what a solar inverter/charger does. >>>
I'd suggest asking the manufacturer - they're UK based.
He seems to want exactly what happens when a motorhome etc is used on rCyhook
uprCO ( parked and connected to the mains).
internet ONT and router plus the VOIP phones working if we have a
power failure. I have a (retired from boat) 12v 100Ah leisure battery providing power to the router, ONT, etc. I thus need a charger which
will keep the battery charged while it's powering the various devices.
The total drain is probably only about 3 amps so I don't need anything
as powerful as most boat/motorhome installations would expect.
Chargers on motorhomes etc are, essentially, fit and forget- or designed to >> be. True they have displays etc on the control panels but most owners have >> little idea what is going on.As on my boat, solar panels feeding an excellent Votronic MPPT charger
that keeps the batteries charged when we're not there and, in the
summer (when we are) it provides much more power, as required.
Votronic do make motorhome mains chargers but they're over -u300 for
the smallest one (15 amps which is much more than I need anyway).
I just need a fairly low power charger (say 5 amps) that will watch
the battery voltage when it gets to maintenance/float mode and keep
the voltage a a suitable float level.
On Sun, 4 Jan 2026 09:21:56 +0000
Chris Green <cl@isbd.net> wrote:
I thus need a charger which
will keep the battery charged while it's powering the various devices.
The total drain is probably only about 3 amps so I don't need anything
as powerful as most boat/motorhome installations would expect.
And that's the issue: you need a device that will charge the battery
*and* provide power to the load.
A battery charger is normally a current-driven device now, and it
monitors the battery voltage. If an unspecified load is also drawing
current from it, it cannot know how much is going into the battery, and therefore cannot monitor charge state and battery condition. Or at
least, it will, and will come to incorrect conclusions.
So a two-output device is necessary, with automatic switching of
battery to load when the mains goes away. I did this on a tiny scale
for a handheld remote controller, with a battery and also external power input. At this kind of power level, it was trivial, with just a couple
of diodes to switch the battery to the load. But with a load in amps, probably proper MOSFET switching will be necessary. The market for such
a device will be much smaller than for a straight charger, hence the exorbitant price.
Chris Green wrote:
Brian <noinv@lid.org> wrote:
Yes, (OP here) I do. It's actually for a 'UPS' at home to keep the internet ONT and router plus the VOIP phones working if we have a
IIUC the OP is after something that'll provide above-float charging while the
battery's in use. It's something I looked for in the past but couldn't find.
And as the OP points out, it's exactly what a solar inverter/charger does.
I'd suggest asking the manufacturer - they're UK based.
He seems to want exactly what happens when a motorhome etc is used on rCyhook
uprCO ( parked and connected to the mains).
power failure. I have a (retired from boat) 12v 100Ah leisure battery providing power to the router, ONT, etc. I thus need a charger which
will keep the battery charged while it's powering the various devices.
The total drain is probably only about 3 amps so I don't need anything
as powerful as most boat/motorhome installations would expect.
Chargers on motorhomes etc are, essentially, fit and forget- or designed toAs on my boat, solar panels feeding an excellent Votronic MPPT charger
be. True they have displays etc on the control panels but most owners have >> little idea what is going on.
that keeps the batteries charged when we're not there and, in the
summer (when we are) it provides much more power, as required.
Votronic do make motorhome mains chargers but they're over -u300 for
the smallest one (15 amps which is much more than I need anyway).
I just need a fairly low power charger (say 5 amps) that will watch
the battery voltage when it gets to maintenance/float mode and keep
the voltage a a suitable float level.
I've used these dumb auto-switchover PSUs for a slightly similar application: https://www.aliexpress.com/item/32843046784.html
I'm after a mains powered battery charger that will maintain a 12v
lead-acid bettery at or near the ideal 'float' voltage while the
battery is in use.
Yes, (OP here) I do. It's actually for a 'UPS' at home to keep the
internet ONT and router plus the VOIP phones working if we have a
power failure. I have a (retired from boat) 12v 100Ah leisure battery providing power to the router, ONT, etc. I thus need a charger which
will keep the battery charged while it's powering the various devices.
It's not **that** difficult, all the charger has to do is monitor the
battery voltage and keep it at the 'ideal' 13.5 volts or so by varying
the current it outputs (the charger that is).
Brian <noinv@lid.org> wrote:
Yes, (OP here) I do. It's actually for a 'UPS' at home to keep the
IIUC the OP is after something that'll provide above-float charging while the
battery's in use. It's something I looked for in the past but couldn't find.
And as the OP points out, it's exactly what a solar inverter/charger does. >>>
I'd suggest asking the manufacturer - they're UK based.
He seems to want exactly what happens when a motorhome etc is used on rCyhook
uprCO ( parked and connected to the mains).
internet ONT and router plus the VOIP phones working if we have a
power failure. I have a (retired from boat) 12v 100Ah leisure battery providing power to the router, ONT, etc. I thus need a charger which
will keep the battery charged while it's powering the various devices.
The total drain is probably only about 3 amps so I don't need anything
as powerful as most boat/motorhome installations would expect.
Chargers on motorhomes etc are, essentially, fit and forget- or designed to >> be. True they have displays etc on the control panels but most owners have >> little idea what is going on.As on my boat, solar panels feeding an excellent Votronic MPPT charger
that keeps the batteries charged when we're not there and, in the
summer (when we are) it provides much more power, as required.
Votronic do make motorhome mains chargers but they're over -u300 for
the smallest one (15 amps which is much more than I need anyway).
I just need a fairly low power charger (say 5 amps) that will watch
the battery voltage when it gets to maintenance/float mode and keep
the voltage a a suitable float level.
On 04/01/2026 09:21, Chris Green wrote:
Brian <noinv@lid.org> wrote:
Yes, (OP here) I do. It's actually for a 'UPS' at home to keep the internet ONT and router plus the VOIP phones working if we have a
IIUC the OP is after something that'll provide above-float charging while the
battery's in use. It's something I looked for in the past but couldn't find.
And as the OP points out, it's exactly what a solar inverter/charger does.
I'd suggest asking the manufacturer - they're UK based.
He seems to want exactly what happens when a motorhome etc is used on rCyhook
uprCO ( parked and connected to the mains).
power failure. I have a (retired from boat) 12v 100Ah leisure battery providing power to the router, ONT, etc. I thus need a charger which
will keep the battery charged while it's powering the various devices.
The total drain is probably only about 3 amps so I don't need anything
as powerful as most boat/motorhome installations would expect.
Chargers on motorhomes etc are, essentially, fit and forget- or designed toAs on my boat, solar panels feeding an excellent Votronic MPPT charger
be. True they have displays etc on the control panels but most owners have >> little idea what is going on.
that keeps the batteries charged when we're not there and, in the
summer (when we are) it provides much more power, as required.
Votronic do make motorhome mains chargers but they're over -u300 for
the smallest one (15 amps which is much more than I need anyway).
I just need a fairly low power charger (say 5 amps) that will watch
the battery voltage when it gets to maintenance/float mode and keep
the voltage a a suitable float level.
Now you've told us more about the likely load etc, I'd suggest something cheaper and simpler- if you have access to a voltmeter.
Buy an adjustable PSU off Ebay - look for one rated at around 15V and
5A. You also need a silicon diode, rated at 5A and 50V min.
Put the diode in series with the positive output of the PSU with the
'arrow' symbol 'pointing' towards the battery +ve.
Before turning on the Power, turn the output pot on the PSU down.
With the voltmeter across the battery (NOT the PSU) and set to a range suitable to measure around 14V, turn on the power.
Now adjust the output pot until the meter reads 13.5V.
13.5V is the 'low end' of the float voltage range, which is 13.5 to
13.8V, for a nominal 12V battery*.
Check the voltage from time to time, over the first few days. If the
needed adjust once the battery charges (if needed).
The diode is to prevent damage to the PSU in the event of mains failure- some PSUs don't like an external voltage being applied. It may not be required, it is a precaution.
I've used the above approach in the past (although in higher current situations) without problems.
* Stay in the 'float range' and the battery shouldn't gas etc. Staying
at the low end allows a margin of error.
On 04/01/2026 14:18, Chris Green wrote:
It's not **that** difficult, all the charger has to do is monitor the battery voltage and keep it at the 'ideal' 13.5 volts or so by varying
the current it outputs (the charger that is).
All you need, is a very basic charger, with a fixed voltage output, and
a more than adequate current rating, to cope with the full, constant
load, whilst on charge - nothing really complicated about that.
Running at that 13.5/13.8 volt level **permananently** isn't good for
the battery, one needs to do a refresh to 14.4 volts occasionally to
keep the battery in good shape.
On 09/01/2026 11:07, Chris Green wrote:
Running at that 13.5/13.8 volt level **permananently** isn't good for
the battery, one needs to do a refresh to 14.4 volts occasionally to
keep the battery in good shape.
What I have always understood, is that charging to 14.4v, squeezes the
last bit of charge into the battery, at the expense of additional
battery wear. Fine, if you plan to need to use that extra immanently,
but not necessary to simply maintain a battery.
On 09/01/2026 11:07, Chris Green wrote:
Running at that 13.5/13.8 volt level **permananently** isn't good for
the battery, one needs to do a refresh to 14.4 volts occasionally to
keep the battery in good shape.
What I have always understood, is that charging to 14.4v, squeezes the
last bit of charge into the battery, at the expense of additional
battery wear. Fine, if you plan to need to use that extra immanently,
but not necessary to simply maintain a battery.
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