Battery Vs battery pack

[rufusgti]

Hi
I have a 1990 Porsche 944 S2. I replaced the battery around 2 years ago with a Lion battery from euro car parts.
The car seems to drain the battery if it's left for long periods, 2 to 3 weeks and the battery will be dead. I have an optimate charger that I sometimes plug in to revive the battery and leave it on for a few days. Always does the trick.
The car has always been slow to start, like the battery is trying to spin the moon. I googled this when I first had the car and it seemed to be a 944 thing. Suggestions of cleaning up some earth's come to mind.

Anyway, I have one of these frankly incredible little Amazon lithium booster boxes that don't look like they could start a hairdryer but it's amazing, always starts the car, and when I plug it in the starter motor turns full speed like a modern car. Even on full charge the car battery never spins the starter that quick.

My question is, is my battery dying. Why is it so slow to start the car. If there's issues with the earth straps etc would the booster pack not be exactly the same. What is the best way of deciphering wether the battery is finished.
Many thanks
Rufus.

[GreenV8S]

You can measure the voltages at the starter motor and at the battery while cranking the engine to see whether the battery is able to supply enough current and whether there is a wiring fault. You can also get the battery load tested. Lead acid batteries don't like being deep discharged. Even if the original problem was not a faulty battery, the battery may now be damaged and need replacing.

Your lithium booster box may be putting out a higher voltage than the nominal 12V lead acid battery. For example a 4S LiPo pack would put out about 14V.

[rufusgti]

Great, thanks. I think I need to get a multimeter for jobs like this.

[tapkaJohnD]

Certainly you need a multimeter, really the first and cheapest bit of kit any car owner who wants to do anything electrical to their car should get.
But not first of all to check the battery volts, but to find out where they are going.
If your in-car battery drains, they are going somewhere, and the m'meter will show you where.

Set it to the 20V DC range and check battery volts while you disconnect the various parts of the loom. The fuse box is a useful place to start. When you disconnect the drain, the battery volts will jump up a bit. Then pursue the drain down the loom until you find it.

People often suggest courtesy lights, radios, clocks, which are all possibilities, but most likely is worn insulation somewhere.

JOhn

[E-bmw]

TBH if the "attached" battery turns the car over slowly & another one turns it over much faster, do you not think you have found the actual problem?

[V8RX7]

Run a GOOD set of jump leads from your battery to the starter motor (positive) and the engine (negative)

If it's any better you have an earth issue

[rufusgti]

Some brilliant suggestions here. Will be doing all of the above.

[rufusgti]

V8RX7 said:

Run a GOOD set of jump leads from your battery to the starter motor (positive) and the engine (negative)

If it's any better you have an earth issue

Where do I find the engine negative? Or do you mean clamp on to the engine for an earth.
That's a bit of a problem as the starter is at the back on the trans and the engine at front. Or can I just clamp to the trans.
Sort if these are stupid questions.

[finlo]

Any accessible point on the engine or gearbox.

[GreenV8S]

finlo said:

Any accessible metal point on the engine or gearbox.

Fixed that for you.

[V8RX7]

rufusgti said:

Where do I find the engine negative? Or do you mean clamp on to the engine for an earth.
That's a bit of a problem as the starter is at the back on the trans and the engine at front. Or can I just clamp to the trans.
Sort if these are stupid questions.

I knew the box was at the back but hadn't realised the starter was too.

Personally, if possible I'd get both connections as close to the starter as possible - IE the positive is the thick lead and the neg on clean metal where it mounts

[MatrixXXx]

it could just be the brushes in the starter motor, dirty or not seating properly

[gothatway]

rufusgti said:

the starter is at the back on the trans

Are you sure about that ? Not on my series 2 it isn't. But the battery is (RHD only).

Edited to say that the earth connections are indeed renowned for failing, though it's not a problem I personally have encountered on my series one or series two cars (note : series 2 is NOT the same as S2, which you have ... confusing Porsche terminology there). An after-market alarm is often reported as the cause of a battery drain, as are the glovebox light and a door switch.

Edited by gothatway on Wednesday 13th March 20:12

Edited by gothatway on Wednesday 13th March 20:18

[Tc24]

Coincidentally had a 2 year old Lion battery from ECP fitted to my E46. Would die if left for more than a day despite alternator charging fine.

Looked online, convinced myself there was a parasitic draw somewhere that would undoubtedly cost a fortune to fix, though nothing showed up on the multimeter.

Before going down the route of throwing money at it I replaced the battery with an Exide one which solved the problem immediately. 2 year battery life is pretty poor in my view (the Yuasa on my Civic was 10+ years old before being replaced) but is certainly not out of the question.

[V8RX7]

I recently bought one of these - as I have many cars and many dubious batteries.

It's not perfect - a freshly charged battery will fool it but it is far faster than messing about with a multimeter


https://www.ebay.co.uk/itm/12V-Digital-LCD-Autos-C...