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Ted · 14-01-2020, 09:45

Why is that my engine starts good on ALL batteries (2x140 Ah) and not anymore on the (new) start battery (85 Ah)?

DeepFrz · 14-01-2020, 09:56

What is the CCA capacity of the start battery? That matters much more than the Ah rating.

Pizzazz · 14-01-2020, 10:17

You need a. We starting battery in any case. Meanwhile, if you need to start your engine on a weak battery, one way to make it easier is to lift the decompression levers on some cylinders, start, then drop the levers.

Ted · 14-01-2020, 10:18

CCA (EN) 800A MCA 1000A

DeepFrz · 14-01-2020, 10:28

Yeah, that should do it if it is fully charged. Check the connections at the battery including close inspection of the wire where it enters the connector. Then check to see what voltage drop you are getting between the starter and the battery when the starter is engaged. I guess I should have asked to make sure that the engine actually turns over when you try to start it.

donradcliffe · 14-01-2020, 10:37

Check the voltage across the posts (not the wires) of the start battery--should be at least 12.6v. Then measure voltage when someone else tries to crank the engine.

If voltage between posts is over 11 volts and the engine doesn't crank, you have a wiring problem.

If voltage between posts is less than 10 volts and the engine doesn't crank, you have a battery problem.

Ted · 15-01-2020, 00:43

Start Battery has more than 12.6 Volts. Preheating goes to 12 V. Starting goes below 10 V. The engine cranks shortly but does not run.
(Mainswitch on 2)

Mainswitch on ALL, it starts directly/good.

donradcliffe · 15-01-2020, 22:34

At this point I'd whip out my DC clamp on ammeter and put it on the 400 amp scale. If the starter is drawing more than 200 amps (2000 watts), it could be the problem.

Or you can take the battery to the nearest auto parts or battery store and have them do a (usually free) load test on it. You can also buy a battery load tester from Amazon for $20 in the US.