12 volt battery charging

Hi everyone,

This is my first post.. so please be gentle with me...

I've had an issue with my 12 volt battery. I have the 2010 model and replace the 12 volt battery in 2015. Recently, my range after charging kept going lower and was at 67 km. I thought I might have a bad cell.

However, the car would not start yesterday and I discovered that the 12volt battery was at 6.5 volts. After external charging, it came up to over 13 volts and the car runs fine. More interestingly, the range is now 101 km.

Any thoughts on what's happening? My mate suggest a charging fuse or the dc dc converter..

thanks..

You'll have to test it just like an ICE car--start it up and measure the battery voltage, turn on headlights, AC and fan, etc and monitor if the voltage falls or if the dcdc kicks in to supply the loads and top up the battery, e.g. should be up around 14.4

Something seriously discharged the 12 volt battery. Once the battery falls below 11 volts, I've noticed mine drops fast to 9 volts, at which point my OVMS module alerts of a critical battery. By then, it needs a jump from a charger. I've had this happen two or three times with my primary car Bear. I'm convinced there's something in the car that doesn't always shut down properly and drains the 12 volt battery. The car would sit for two or three days and I'd come home to a dead battery (usually on a trip in the hybrid), but our last trip, the car sat for 3 days and still had plenty of charge in the 12 volt battery.

First thing to is measure the voltage with the car off, car in READY, and car in READY with all lights on, cabin fan in MAX, and rear defroster/heated seat(s) on. The voltage when off should be around 12.8 volts and 14.2 volts when READY, almost regardless of loads. If that all looks good, then the DC-DC converter is fine. Shut the car off, and do a load test on the battery.

Remove the 12 volt battery and have it load tested at a battery dealer. If it's OK, charge it up and let it sit for a day and check the terminal voltage. It should stabilize about 12.5 volts if all cells are in good shape. If you have any question about the battery, replace it again. Buy the best battery that will fit and if you really like your car, put in an AGM battery and rid yourself of the flooded lead-acid battery. It really needs a deep cycle battery and not the normal starting battery that most people have in a ICE car. As far as the car's DC-DC converter is concerned, simply put the car in the ready mode and see what the terminal voltage is at the 12 volt battery. I should be in excess of 14 volts. If the DC-DC converter was having problems, you would not be able to travel very far before the car would quit. You would have a battery warning light any time the car was in the ready mode and possibly a MIL. The 12 volt battery is the very worst part of the I-MiEV experience IMO. The original was never very good. You should also invest in a trickle charger and keep the 12 volt connected to it any time the car is going to sit for more than a couple of days. Some of the power electronics are active at all times and take energy from the 12 volt battery. You need a battery with high reserve capacity, not cranking amps (hence deep cycle). There are junk batteries out there but the factory I-MiEV 12 volt seems to take it to a whole new level :twisted: .

Thanks everyone for the good info. The DC DC converter does seem to be working as the voltage is over 14 V in the car is armed. I will test the battery and it makes sense to make it a deep cycle battery. The car was left for a couple days so the fact that some electronics could be on all the time doesn't make sense for a depleted battery. Why only for the question is why the range was reset to where it was about when I bought the car?

It's possible that some battery health info was lost or reset with the run down 12 volt battery. I noticed when I took my car to the dealer that if they had to reboot the car's computer, it always said 74 miles RR when I picked it up.

Did your trip odometers reset to 0 when the battery went dead?