Morris Minor Owners Club

Sorry nothing to do with Minors. My battery is on charge in the garage, I want to leave it on until late, I have a heavy cable capable of coping with power and lights, travelling underground from garage to consumer unit in house. Instead of walking to the garage at midnight, to turn off the charger, I see no problem in switching off the supply to the garage from the unit. Is this in order ? I also presume there is no detriment, with the charger still being connected to the battery when power is off ? Reading this post back, It sounds relatively obvious but I’d like reassurance please.

The Charger diode arrangement should stop the battery discharging via the Charger being left connected but not powered up.

I understand where you're coming from though.

If you want to prove it to yourself, just go out there now and switch the power off at the charger mains plug, whist leaving the connections to the battery in place.
If nothing has caught fire or melted after a minute or two, then you're good to go.

Im grateful for your reply, I’ll do as you suggest but I don’t like the sound of the possibilities, if things are ok after a few minutes it’s pretty reassuring and I don’t doubt your experience of all things electrical but I couldn’t handle the remote possibility of a failure at some point after. I’m a piece of mind type of guy.
Your post has helped me decide, despite the remote possibilities. Thank you.

Les I do this regularly, my garden water feature and my shed are both on the same power supply. In the shed my bikes are on battery minders ' optimate, often if I have forgotten to switch off the fountain I just switch off the supply from in the house to save going out to switch off the fountain. So like you turning off battery chargers while still connected, I have done this occasionally over 9 years and never had an issue. Just power back on next day and chargers back to work.

Thanks Bill, good to know, it’s just my vivid imagination playing games !

What happens if the mains fails? Absolutely nothing - or there would soon be fires reported all over the place!

oliver90owner wrote: ↑Thu Sep 04, 2025 11:04 pm What happens if the mains fails? Absolutely nothing - or there would soon be fires reported all over the place!

I think Les was referring to damaging the battery maybe rather than causing a fire

Bill_qaz wrote: ↑Thu Sep 04, 2025 11:49 pm

oliver90owner wrote: ↑Thu Sep 04, 2025 11:04 pm What happens if the mains fails? Absolutely nothing - or there would soon be fires reported all over the place!

I think Les was referring to damaging the battery maybe rather than causing a fire

Does your mobile phone discharge, if the power supply is shut off? I wouldn’t think so in any scenario (other than the unlikely failure of the phone or charger).

I asked the question to get opinions from those who know electrics better than me, and received informative answers. I wasn’t expecting an element of sarcasm from a certain poster but perhaps I should have done.

"Does your mobile phone discharge, if the power supply is shut off?"
Of course it does, if switched on, and just lying idle in stand by. It might take a few days, depending on battery capacity, if not used. That question isn't relevant.

The charger may well have a diode in its final output circuitry, to prevent a reverse current into it from the battery.
But these days the circuit diagram is probably not published.
Alternatively put a test ammeter (DVM on a high current setting) in series with one croc clip lead, and see if it registers any backwards current with the charger turned off.

Thanks for sharing that method of checking, Mike.

Mervin wrote: ↑Fri Sep 05, 2025 3:52 pm "Does your mobile phone discharge, if the power supply is shut off?"
Of course it does, if switched on, and just lying idle in stand by. It might take a few days, depending on battery capacity, if not used. That question isn't relevant.

Yeah, right. Not exactly likely to cause a fire or discharge a 550Wh battery, is it.

Yet another scenario from inside the box. Alternators charge the battery on most cars, these days (but I have neither an alternator nor a DC dynamo to charge my car battery). Does the battery discharge more than the normal ‘discharge over time’ when the engine is turned off? That should provide the answer to the OP’s original post, I think.

Unless I've missed something, the OP hasn't told us why the battery needs frequent charging.
Only that his question was "nothing to do with Minors".
So he's not reporting an issue with his battery inexplicably discharging.
So is the battery even in a car? Perhaps just a spare, or in a caravan?
In any case I'd have thought a little-used battery would need only an overnight top up once a month.