Help! Our car was stopped in an intersection and was hit from behind. The bumper needed replacing, but the car also stopped running and wouldn’t start. It was towed to the garage and the mechanic said the alternator was fried and the battery was dead.
The mechanic said the alternator and battery damage was caused by the accident. However, the insurance company claims the alternator damage could not be caused by the accident and refuse to pay for the repair or the associated rental car.
Can anyone shed some light on this? Who’s right?
Was the car running at all after the accident or did it die immediately?
The car die immediately and the steering wheel froze.
Given the info you provided and having 24 years experience in fire/rescue as well as fleet maintenance … I suspect the impact dislodged the plates inside the batter (power surge followed shortly by an internal short) which can very well cause the alternator and most everything else electrical/electronic to fry - save all the old parts and have the wrench do a complete operational diagnostic test on the entire vehicle to see if anyhing else is screwed up. Do not talk to the insurance company any more, nothing, not a word, neither you nor your wrench and for dang sure do NOT let them have the old parts! All correspondence in writing, if they continue with the attitude, spend some extra money and have the parts damage confirmed by an independent shop or the dealer then take the insurance company to court.
All this is speculation in that we can’t see the car, but a big hit in the rear end could have shaken up the battery internally and shorted it out. A shorted battery could put a current surge into the alternator and cause it to fail. How likely is all this? Not very, but could it happen - yes. It seems the insurance company should pay for repairs for not just the visible body damage, but to also put the car back in running condition.
This insurance company is playing hardball with you. Your choices, depending on the cost of this repair, is to hire a lawyer to lay out your side in a letter, with a notarized statement from the mechanic stating in very precise terms why the alternator and battery failed.
Second choice would be to invoke your collision coverage (if you have it), work with your insurance company for the repairs, and then let the insurance company lawyers fight it out. You stay on the side lines.
Third choice, if the expense isn’t great, is to pay the bill and move on with your life.
Yes, the alternator and battery can be damaged by a collision just like anything else on a car. I’ve seen transmissions and engines that did not have an external mark on them anywhere and yet suffered severe damage due to an impact. (One of them was a car that belonged to me.)
Tell the insurance company you’re suffering some headaches and stiff neck lately and I’d bet they may have a change of heart, along with wanting you to sign a release form after the new battery and alternator of course. 
Thank you all for the info and advice. If I have it right, the battery could have shorted out with the impact and the resulting power surge could have fried the alternator. The situation is unusual but possible. The parts may confirm that theory. The parts need to be examined by an independent third party to explain what happened.
Thanks again.
Your insurance company should be shaking down the insurance company of the person who hit you.
Good point. We’ve been talking to the other insurance company directly. Maybe we should let our insurance company do some fighting for us. Thanks
Get a signed statement from the mechanic stating that the alternator was, without a doubt, damaged by the accident. Actually, get two different mechanics to sign a statement affirming the same. Hire a lawyer if you can afford it, and don’t let your auto insurance company get away with this!
It seems that as soon as a car is involved in an accident it merges into another dimension where one in a million events are as common as rocks on the side of the road. America is infected with this concept of an accident making the obscure the most likely.Sorry to say it is correct for the insurance company to deny this claim, how do they know that the car was not damaged by a reverse polarity jump at the body shop (which is much more likely that the battery plates getting knocked loose).The simplest explaination is likely the correct explaination.
For future reference, NEVER talk to the other guys’ insurance company directly. File the claim with your insurance company and let them duke it out with them. That’s what you pay them for. The only people who should be talking to his insurance company are your insurance company or your personal injury attorney.