Starter motor won't engage... help with steps to diagnose

I think there may be different charging methods, but the one I know some "intelligent" chargers use, is to apply constant current until the voltage reaches a certain value, say 14.4V, then the charger applies constant voltage for some time until the current drops to close to zero.

Cheaper chargers may just apply a constant current with voltage limiter of 14.4V (or similar). The effect is about the same as with a more intelligent charger.

Just measuring the voltage on a battery will not tell the truth, you have to put a load on the battery or try to charge it with a certain current.

 

Cheaper chargers (including some trickle chargers) will just keep charging a battery until it possibly catches on fire. Just an FYI for anyone using those things. Be sure you're doing it safely.

 

Totally concur! I do not use unattended chargers for that exact reason. I had two such incidents many years ago so now, when a vehicle (car or Moto) is not going to be used for several months or more, I disconnect the battery. I have left my 328 in that condition for as long as 7 months and, upon reconnecting the batt, it spins the starter/starts car with no issue at all. The normal battery self-discharge over that period of time has never caused a battery to be too low in capacity to start. I use smart chargers but only when I am able to routinely check them.

My use of the term, "Unattended" means that the vehicle is located where I can't conveniently/regularly check the charger/batt. For example, I'm in the UK for 5 months; the car is in TX.

 

This exact syndrome was happening to me several years back.. on my 400i. It turned out to be three things. That big ugly Italian starter with its internal gear was not disengaging completely from the flywheel due to a bent shaft, due to a worn out solenoid, due to not enough juice getting to it due to a loose battery-ground with a corroded cable. The solution was to ditch that old slow cranking starter for a brand new high torque pug-and-play starter. Also....replaced all of the battery cables with marine grade cable form the boat store that I made myself. When I did an autopsy of the old original factory cable, it had so much corrosion running through it, that even the new battery couldn't pump enough juice through it to properly engage the solenoid, thus destroying it. It's not your battery with 12 plus volts (measured at the battery), it's the cables. Since swapping out for a new starter that turns the engine over within 2.5 sec., problem solved. The best $500 bucks I've spent on her. I truly hopes this of some value to someone. You can rebuild the old starter and keep it for (concours), or sell it, as they fetch from $500-900, as they are original to many older models clear across the board. I hope this is useful to someone. Thank you. Jq.

 

For what it's worth, I'd check the grounds too. I had this exact problem and removed the ground from the block to the frame, cleaned it and put it back, problem solved. A slightly weak battery may not have enough juice to overcome a slightly bad ground where a fresher one might have just that much more juice. Just my $.02.