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Down-sizing starter battery?

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Hello,

 

my Alvis Shielder's batteries are stuffed (they are the UK6TNMF or UK6TN's). They are an unusual shape (almost square) so to replace them is difficult.... I've been looking at smaller batteries that would still fit in the battery tray. If I stick to the same or larger CCA rating does it matter if the replacements have a smaller capacity (AH rating)? Specifically the originals are 800 CCA and 110 AH and what I have in mind is 880 CCA and 60 AH....

I'm not likely to start the engine multiple times in a row or use power with the engine off.

Thanks in advance for any opinions!

Cheers,

Steve

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We had a CVRT that came with a pair of the smallest possible civilian batteries on it, and they were fine for our use including re-commissioning the vehicle (multiple starts) and electrical fault finding (powered up but not running). They were still on the vehicle when we sold it a couple of years later. I think one of the reasons for the large military batteries is due to them being required for powering radios and also standardisation. You'll find the same batteries on most 24V ex-MOD vehicles from Land Rovers to lorries and AFVs, so they need the capacity to be able to power the largest. Personally i'd fit the largest you can fit or afford. Just ensure they are properly secured and that the terminals are the same type. I've seen vehicles with round post cable clamps on flat post batteries!

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Thanks for the replies. I suspected there would be no problem as long as the CCA was similar but I had a nagging feeling that maybe a smaller battery wouldn't like being charged by the bigger alternator, ie get charged to fast.

Those Varta J3s are not sold here in Australia. I'm considering the North Star AGM35 due to its compact shape:

https://batteryspecialists.com.au/northstar-pure-lead-12v-60ah-880cca-agm-battery.html

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I've been running MUCH smaller batteries in my vehicles for years for a variety of reasons, weight reduction on smaller vehicles is the most common.  In all cases, I've had no problem at all with battery life or charging system issues.  If you have parasitic loads or engine troubles it will become apparent much more quickly (don't forget and leave your lights on)  and I wouldn't try it in very cold climates.  I should say I've been using odyssey batteries which are a high-current non-liquid battery so that might be some of why it works so well.  Two of their PC925 crank the Cummins lump in my CVR(T) with no problem at all and they take up very little space so are easy to move in and out of the hatch.

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I keep an eye on batteries in our fleet of about 60 old military vehicles, including 5 Ferrets. Many of the older vehicles like the Ferrets have gas engines with low compression ratios around 6:1 which really reduces cranking amps compared to more modern cars with greater than 9:1 CR. And of course the 24v supply cuts the cranking amps in half again compared to a 12v car. 

So an old 4 litre Rolls Royce or Jaguar engine with a 24v system only needs about 100 cranking amps, maybe 150 in really cold weather. So the 700 CCA you get from a pair of decent 12v battery in series gives you a huge margin to deal with long storage periods, prolonged cranking to prime empty fuel systems, etc. 

The highest cranking amps I have seen are on more modern 30 litre diesel tank engines (400-500 amps). Jeeps are the lowest at 50 amps. WWII stuff like universal carriers and CMPs are high at 200-250 amps because of their 6v systems. 

I find most people don't know how to test a battery properly. Getting good voltage across the two posts means nothing. Good tests are: specific gravity of each cell after charging, load testing after charging at half the rated CCA, which needs a carbon pile tester (the load from the cheapy 100 amp heating element type testers is too low), and my favourite, the battery internal resistance tester. 

One benefit of good testing is you can keep even older worn out batteries in service by using them in low cranking amp vehicles like Jeeps. 

We have been buying Deka military batteries and have found they are crap. If they are discharged right down they just won't come back. However, I am really impressed with Pow-R-Surge batteries. 

 

Malcolm

Edited by sexton
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In years past when 12V auto batteries had the exposed cell connections you could check each cell individually with a load tester but those days are gone !

cell.jpg

Edited by goanna

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I agree with Teltech. The Oddesey type batteries are more expensive initially but so much more reliable. I bought one must be about five years back for my Discovery 200tdi that I'd fitted a winch to. It got used on various vehicles since, then due to leaving lights on went totally flat, taken off and forgotten about for a year or so. Then a few months back I decided to recharge it. Charger wouldn't start so I conned it by parralelling a god battery and the Oddesey charged. It is now sitting on a old Discovery 300tdi that I'm modifing with winch and other toys for Winter use.The vehicle gets started perhaps once a week for half hour or so at the moment. Battery keeps full charge and starts the Disco every time. 

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Odyssey batteries are made by Enersys, the same people who make the Hawker UK6TNMF, so I think we can safely say they know what they are doing.  One word of warning, they are very sensitive to charging voltage, which must not exceed 15V for a single battery or 30V for a pair of batteries in series.  If your batteries are dying, check the charging voltage before doing anything else.

Andy

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A CVR(T) fitted with a J60 engine, which is to all intents and purposes an E type engine/XJ6 engine, when fitted in a car has a 12V nominal 66AH battery. Therefore two 12 volt batteries in series @66AH is more than adequate (Cranking amps unknown), however 770A seems to be recommended @12V

AGM cells info =

https://nyln.org/agm-batteries-pros-and-cons-list

Diana

 

Edited by Diana and Jackie

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Beat me by minutes !

Diana

 

2 minutes ago, andym said:

Odyssey batteries are made by Enersys, the same people who make the Hawker UK6TNMF, so I think we can safely say they know what they are doing.  One word of warning, they are very sensitive to charging voltage, which must not exceed 15V for a single battery or 30V for a pair of batteries in series.  If your batteries are dying, check the charging voltage before doing anything else.

Andy

 

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Thanks for the replies everyone.

The Shielder has a Cummins 6 litre turbo by the way.

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My son has a Cummins straight-6 5.9 litre diesel in his 1989's truck. I was curious why the specified battery cables were so heavy so I measured cranking amps. 400 amps with the 12v starter. That is really high. So on a 24v system that starter would take around 200 amps. At that level of current, you have to make sure all the cable and terminal connections are clean and tight.

malcolm

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