Dead - no turn over

[Politted]

1978 Westy bus. Started reliably, then left sink pump on for a week. Jumped it. Drove 15 minutes, shut off, tried restarting, dead. Had to jump again. Drove 10 minutes, shut off 15 minutes, tried starting, dead. Jumped it. drove 10 minutes, shut it off, tried starting, dead. Jumped and drove home. Put on charger for 24 hours. Started ok 8 to 10 times. Then dead 4 out of 6 times. Last couple times, when dead, could point downhill and pop start. I’ve had it back on charger for a few hours, then started right up. Battery only 2 months old. I guess it’s not charging while running??? Only been going on short trips. Wife fretting about not being able to find a hill to park on!! Thoughts?

[Eric&Barb]

Take battery to your FLAPS to have it tested.
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[d___dles]

I may be wrong on this but I had 78 which was fuel injected and read that you shouldn't jump fuel injected VW engines?
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1967 Riveria Camper

[Eric&Barb]

[SGKent]

get a new battery. You sulfated it
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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[aeromech]

Even though it’s your fault, you might be able to get a prorated battery where you originally bought it. Sometimes batteries fail early.
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[Wildthings]

I think it likely that you hooked the jumper cables up backwards and fried the diodes in your alternator. No alternator = no charge = no crank at every start.

Get your meter out and do some testing. Make sure you buy a roll of red tape and mark the positive cable with it and use black tape on the negative cable if it is anything besides black or bare wire.

[mikedjames]

Letting a battery go flat for a week is enough to cause it to sulphate up.

Does not really matter how old it was, you put years of damage on it by leaving it flat.


Even if the alternator charges it, it will show good voltage but have no capacity to start the bus.

When its like that, if the alternator is working it maintains the voltage for the ignition .

Consider using a separate service battery.so your starter always has some power.
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Ancient vehicles and vessels

1974 VW T2 : Devon Eurovette camper with 1641 DP T1 engine, Progressive carb, full flow oil cooler, EDIS crank timed ignition.
Engine 1: 40k miles (rocker shaft clip fell off), Engine 2: 30k miles (rebuild, dropped valve). Engine 3: a JK Preservation Parts "new" engine, aluminium case: 26k miles: new top end.
Gearbox rebuild 2021 by Bears.

1979 Westerly GK24 24 foot racer/cruiser yacht Forethought of Gosport.
1973 wooden Pacer sailing dinghy

[Wildthings]

[Politted]

I’ve completely discharged my share of batteries that went back to normal operation after one full charge or jump… so I was leaning toward bad alternator or starter… I guess a new battery is definitely the easiest fix to try first.

[alman72]

[SGKent]

[Wildthings]

[airschooled]

[SGKent]

the ECU, and the diodes in the alternator, pretty much poof when jumper cables are hooked up backwards. It doesn't help that lots of people install aftermarket ground cables that are red, and the original 12V+ is usually black. Almost have to hang warning signs on the battery as to which is positive and which is negative.

example:

https://rcswag.com/product/battery-polarity-sticker-decals-positive-negative/

or

https://www.stickersmakeyoufaster.com/Polarity_Indicator_p/polarity-indicators.htm
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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[Wildthings]

[busdaddy]

[SGKent]

from what I understand, the battery has resistance to ground when charging. That is calculated into the equation. If the jumpers are reversed then it is a dead short to ground and the battery resistance does not factor in. There are plenty of threads here where the exciter diodes in an alternator popped, and some instantly dead ECU.
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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[Wildthings]

[SGKent]

When the car battery is dead, and a battery is jumped backwards, the electrical system has 12V essentially backwards on it. The dead battery will pull some of the jumpers capacity but the rest will go into the car. There is no war of the batteries in this situation where the current goes round and round in series melting things. If a diode stands between the battery and ground say designed to carry 1/3 the load of the alternator when charging, it might be rated to let's say 400V 75 amps (that is what the NTE 5934 and NTE 5935 that go in a 55 amp alternator are rated to).

Each carries 1/3 so they are rated well above the alternator capacity. Now we hook 12V up to them backwards so the rectifier bridge is reversed, and the current passes thru it in the direction it was designed to flow, but the battery is putting out 400 - 600 amps. The current flowing thru them, which the door is open to it in that direction - the diodes melt internally and open as the junctions overheat internally. Think of it like a door that is designed to withstand 100 PSI from one direction, and allow a gentle flow when 101 or more PSI is put on it from the other side. If the system can only generate 120 PSI max then 20 PSI is the heaviest pressure that will push flow thru the door. But if we remove the 100 PSI pressure on the side that is normally there, and run 120 PSI on the side it is designed to flow then it can be damaged by the massive and sudden flow. That is the best analogy I can think of. When the jumpers are reversed to a dead battery, the alternator diodes are handling all the jumper capacity instead of the max the alternator can put out, which is what they were designed for.

Likewise, I would guess that if one hooked jumpers up backwards to a good fully charged battery there would be one hell of of a spark and something would melt as the batteries were essentially shorted by the jumper cables while they were hooked in series. The same as if two batteries were set in a row, each 12V and the + hooked to the - of the next one. That would create 24V at the current potential of either battery, but not both. Then when the second jumper was attached that would be just like dropping a wrench or wire across them and shorting them at 24V. Totally different scenario than jumping a dead battery.

There is always the risk of battery explosions too when someone does not know the proper procedures for battery jumping. The jumper ground to frame should be last where everyone is out of harms way.
I could be wrong but maybe Telford can chime in and explain it better.
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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin