charge battery in situ

EdGasketTheSecond

sevenhills wrote: »

Just the same as an alternator then?

1) You will never get a problem charging an 'okay' battery
2) you will never get a problem with a decent car charger.

You will however get a problem with a completely flat battery, and I mean flat as a pancake with a charger that doesn't have the ability to sense a dead battery. In this instance the charger increases the voltage to a level sufficent to charge the battery. Its this raise in voltage that will potentially harm you cars electrics. I would monitor the voltage and anything up to 14v will be fine. If the charger gets the voltage up to 18-19v to charge your dead battery something is going to get damaged.

George_Michael

Tarambor wrote: »

It is a good job then that the battery is a huge capacitor which will smooth them out.

Wrong I'm afraid. The battery will not smooth out anything when connected to a charger.
If a battery charger is connected to a battery then as it is connected in parallel, any surges or voltage spikes will still be felt by anything that is still connected to the system (such as an engine ECU).

Try jump starting a car with a 12v system from a vehicle with a 24v system and see how well the battery acts like a capacitor and smooths out the extra voltage.