You could try to charge them in Nimh mode, with a low current like 0.5A or 1.0A for a short moment to raise the cells voltage, let's say 8 or 9volts, and then stop and switch to Lipo balance mode.

If cells have gone too low they shall be really damaged, be careful and always keep an eye on them during charge.

Also check them while running your car, if you succeded in charging them.