Dead battery?

Went to start my Thundercat today but after sitting for a few months it wouldn’t turn over. Starter motor ‘tried’ to get going but not enough juice.
Got the jump leads out and got it going. Gave it a wash while I was waiting for it to get charged up.

After about 15 minutes I cut the engine and tried starting but this time the start motor didn’t even try to turn. Just silent.
Light on dash looked fine, slight dim when I hit the start button.
Weird. Jump started it again (obviously the started motor turned over this time) and went for a ride.
Got back after 20 minutes, turned engine off and on again, same thing dead as a dodo and no starter motor.

So… Have I knocked some fuse or lead, or is the battery just dead? I don’t understand why the starter motor was trying to work, but after the bike had been started for a bit, stopped and started again it wouldn’t try to start?

Thanks for any advice :slight_smile:


could be reg rec; put a meter on it see wot it reads

Good luck

sounds daft but have you checked the terminals on the battery? mine worked their way loose last week and I got intermittent power failures for the ride home

Was going to say the same thing about the battery terminals too, mine was doing the exact same thing a couple of weeks ago. Also make sure the batterys charging when the engines running.

Deep discharge can permanently damage a battery, especially if the battery is allowed to get very cold whilst deep discharged, It is possible a cell is now duff so the battery will not generate 12v.

On the other hand, this could be a charger problem, or a rectifier problem.

  1. Check the battery terminals are clean and properly connected.

  2. Check the battery has fluid. If the cells are very low or dry the regulator has failed and fried the battery.

  3. Measure V across the battery. Anything below 12v and it is not charged. If it is 10 or below it is probably toast due to a failed cell.

  4. Measure V across battery with engine running. V should start about 12.5 and as you increase revs the V should rise to between 13.5V and 14V and stop there. If they continue rising the regulator is dead. If the V do not get to 12V or start at about 12V but fall as the revs rise, the generator is faulty or the regulator has failed. This can be as simple as a corroded connector, but other tests are necessary to sort out exactly what the problem is.

Great thanks for all the information chaps.
I’m borrowing a multimeter this afternoon so will give it a test and see what it says and feedback this evening :slight_smile:



Hi guys,

Yeah didn’t get cold while uncharged as far as I’m aware, its been pretty warm down London way.
Anyway gave it a test and its pretty dead. Showing about 7.5v so I got a new one ordered.
I’ll do some further tests over the weekend to check the generator / regulator with the engine running.


It does sound like it’s a battery problem. Did you manage to resolve it Rob?