Battery dead, PS light (among others!) coming on

[EddieM]

I have three cars in family, and since March hardly used, so been using a couple of Lidi smart chargers to keep battery topped up, and out of interest used an energy meter so I could see when charging complete.

What became clear was it takes a long time to recharge the battery, time not miles, talking about days, not hours, the first bit would go in fast, but at the 0.8 amp rate could take 10 days before it finally dropped to 0.1 amp rate, so your not going to drive for that long, only option is a smart charger for an extended time.

As you've said, no one drives for days, so if you have a battery in reasonable condition, a couple of hours charge every week would be fine.

 

[Harry Bloomfield]

As you've said, no one drives for days, so if you have a battery in reasonable condition, a couple of hours charge every week would be fine.

My also little used car, is in the garage, receiving a 20 minute daily boost on a dumb, but voltage limited charger. Dumb so no buttons need to be pressed to start the charge, yet it offers no discharge to the battery when left connected. It is powered from a Smart Plug, switched on and off by Alexa via wifi.

My system has only been in place for a few months, but so far all good and in time I might extend the idea to keeping the caravan's leisure battery topped up

Last week, I added Christmas lights to Alexa control via Smart Plugs for the first time. I usually run them via plug in timers.

 

[ericmark]

With a switch mode power supply and 13.2 to 13.4 volts a 12 volt battery could be left on for an extended time the batteries in fire alarms, intruder alarms, stair lifts and like can sit on a charger for years, but as the voltage increases so the time on charge needs to reduce, so 13.8 is about the limit for 24/7 charging.

However those who remember the dynamo will remember the equalising charge, very low rate, left on charge 24 hours and topped up after with distilled water. Idea was not all cells are the same, so you over charge some cells so the low cells are fully recharged. This is where the so called smart charger is better than the fixed voltage, as it in essence switches on/off or up/down charge rate, so battery raised to 14.4 volt, then the charger switches off or down, and voltage drops to 12.8 volt at which point it raises the charge rate again, so the voltage spikes do the equalising bit.

Well that is the theory anyway, there is also a school of thought that pulsing the charge can damage the battery, so half a dozen of one and 6 of the other, however my experiment with heavy sulphated battery did show it can take two weeks to recharge, what was a surprise was not gradually over two weeks, but nothing for 10 days, then fully charged in the next 4 days.

The caravan battery now at the house, our normal method would have been to swap caravan battery each time we went up, but since can't use caravan we have both at home at the moment. So 5 car size batteries, 3 smaller ones for jump start unit and mobility scooter, and some small 7 Ah ones from old stair lift etc. So the chargers are always on one battery or another.

I suspect my Kia battery is on the way out,

all other batteries settle down and show a voltage over 12.8 at 0.1 amp, but the Kia battery has been switching between 0.1 and 0.8 charge rate for weeks, after I allowed it to go very low. Or the is some thing left switched on in the car which I have not found.

 

[Harry Bloomfield]

With a switch mode power supply and 13.2 to 13.4 volts a 12 volt battery could be left on for an extended time the batteries in fire alarms, intruder alarms, stair lifts and like can sit on a charger for years, but as the voltage increases so the time on charge needs to reduce, so 13.8 is about the limit for 24/7 charging.

I would suggest from my experience that your 13.8v as the upper limit for 24/7, is still to higher than I would like for a permanently on charge battery.

My caravan's PSU runs at 13.8v and I leave that on year round, but with the battery isolated. Every so often, for a day or two, I reconnect the battery to bring it back to full charge. Before a trip and if I remember, I try to put the battery on a smart charger. Battery capacity remains great and now 10 years old. Mostly it is there to provide power for the mover.

 

[ericmark]

I have noted that AGM batteries have a higher voltage recommended to normal sealed for life, that seems odd.