My daughter’s Audi started fine this morning and come end of work shift the battery is dead. No lights on, doors open, etc. I’m going to go do the jump and then she will drive home for a charge. I have a Solar 500 HD Battery Charger from back in the day. How many minutes charge at 12V Medium before doing the readings to see if the charge is holding?
The battery is an odd looking duck so I am motivated to ask what might be odd about charging this thing.
I can’t give you the specifics you want, but in general it takes about 8-12 hours to fully charge a deeply discharged lead-acid battery.
My suggestion is to let it charge until it starts then run it for 20 minutes or so and let the brains of the system do their job. If that is the original battery you might as well replace it. It could be a new battery drain symptom but start simple and work your way up. In general I am in a hurry and use the fast charge setting that will do the job in 20 minutes max. If it is an old battery that needs replacement, what do I care.
I can imagine a lot of batteries having a short life if they only get 20 minutes to charge. Unless you’re driving cross country the cars charging system will take days or weeks to do the job, and that’s too long.
Thanks for everyone’s reply. My patience forever messing with my daughter’s car drove me to the high boost, but I understand the need for longer charge. Checking the good vehicle records and find that it is original. So it’s running and holding at 100% now but will very soon be retired from it’s 9 year run. She’s moving and Dad is not going to be a cell call and 10 minutes away.
Most car batteries are around 50AH capacity…Bigger cars maybe 75 AH… Most alternators can provide at least 10 amps, so it would take them 5 to 7 hours from stone dead. Your charger must have an amp meter on it…Figure 3 hours at 15 amps. When the battery gets warm to the touch, that’s enough, or reduce the rate to 5 amps…
Nine years?? Don’t waste your time…
Ditto…
The thing is the battery will not take the full current during the whole charge.
There is some temperature dependence but basically charge voltage should never exceed 16 volts. Any more and most of the energy goes toward generating gas and heating the battery. Charging a typical car battery at room temperature and a steady 15V the charge current will taper off to ~1 amp or less as the charge reaches 100%.