Charging Battery

Feria40 · 27-02-2022 9:56am #1

Hi all

I have a flat battery. Tried to use my battery charger but it won't work as battery is too low.

I tried connecting the battery up to my own car to get some residual charge into it but it looks like the voltage dissipated quickly once disconnected.

Due to the way the other car is parked, jump starting is not an option.

The battery is less than a year old but car was parked up for a couple of months and even prior to that wasn't in exactly every day use.

Am I asking for trouble reconnecting the battery to the battery charger AND connecting the battery to my own running car with jump leads simultaneously...

This sounds nuts to me so just to say it's not my idea!!

10-10-20 · 27-02-2022 10:15am

If the battery is that low, you might be in trouble. Perhaps you have a faulty cell. What voltage it it showing?

The way that I've recovered very flat batteries is as you described - I charged them in parallel with another battery. That way the meter reads a sufficient voltage and hits the flat battery with ~14v. I have had good success with this method, but you have to be aware that you can boil the battery this way. Boiling it would cause the battery to vent off an explosive mixture so it needs to be done in a well ventilated area.

Try it out by charging it in parallel with another battery for 20 mins and then disconnect it and check the voltage. If it drops rapidly back below 10v, then it's bust.

27-02-2022 10:17am

"Jump start" the battery charging by other 12V battery. Charge short time (5 min) two batteries parallel and disconnect charger and other battery. Now you can charge only empty battery.

Feria40 · 27-02-2022 10:19am

When charging in parallel with another battery is the car in which the other battery is sitting running?

Feria40 · 27-02-2022 10:19am

27-02-2022 10:30am

https://www.boards.ie/discussion/comment/118701534#Comment_118701534

I did not said any word about other car. Sure, you can "jump start" the charging by other car. All what you need is about 8V to start the battery charger. Do not use battery charger if you use other running car for voltage boosting. Also do not try to crank the car where is empty battery, you can ruin 2 cars. For cranking you need to charge the battery at least 10 minutes. Be sure the battery have enough ventilation (open the hood or trunk, where ever the battery is mounted), because empty battery accept load of amps and can generate big amount hydrogen gas. Disconnect the battery ventilation hose, it is designed for running car, not stationary car. Remember to connect it back later. Do not smoke!

If you do not have any other car or battery, you can use 12V power supply for short time (only if battery is removed from car or negative lead disconnected). Even half amp 12V power supply works, just takes bit time. It helps to rise the voltages above 8V. Do not use the power supply and the charger together - power supply burns down.

02-03-2022 4:52pm

https://www.boards.ie/discussion/comment/118701534#Comment_118701534

I have the same problem with the lawn mower each winter.

Go to charge it and the battery charger thinks is a 6 v battery.

Pair of jump leads to another battery to fool the charger into believing its 12v. . Connect charger and it starts charging. Then disconnect the good battery and it will continue to charge the bad one.

Regarding jump leads , you can get 6m jump leads. Ive a set of 6m 1000amp jump leads and they are very useful, as you can jump stuff start stuff in tight corners. I would recommend a set