Battery capacity

[BruceB]

I need to buy a pair of batteries for my console. My manual says I need a 100AH battery for my 90HP.
I am fitting both a main and a backup battery fed through a switchable VSR, would I get away with two 85AH or 88AH batteries instead of having to buy two 110AH? I am not sure just how much allowance suzi would have made on extra capacity.
Or would I be better just biting the bullet and buying two of the 100AH's?

[Searider]

What's important rather than the capacity is the current that can be supplied for starting. This info might be in the Owners Manual or installation guide.

For example my 150 Optimax needs 750 MCA? CCA? cant remember which. I went to my battery supplier and chose a battery that could supply that. Was a little smaller - lighter and cheaper that I would otherwise bought.

[codprawn]

Originally Posted by BruceB

I need to buy a pair of batteries for my console. My manual says I need a 100AH battery for my 90HP.
I am fitting both a main and a backup battery fed through a switchable VSR, would I get away with two 85AH or 88AH batteries instead of having to buy two 110AH? I am not sure just how much allowance suzi would have made on extra capacity.
Or would I be better just biting the bullet and buying two of the 100AH's?

An 85AH would be fine. If 1 will start my diesel Discovery on a cold morning it will cope with a 90hp outboard easily.

[BogMonster]

Originally Posted by codprawn

An 85AH would be fine. If 1 will start my diesel Discovery on a cold morning it will cope with a 90hp outboard easily.

Yes that is correct. A standard type 072 diesel battery as found in most older Discoverys or Defenders is only about 70AH but produces 600 amps which if it will turn a 2.5L diesel easily, will certainly not have a problem with a petrol engine of anything up to about 4.0L. My 115hp is 1.8 litres I think, and the current battery is not an 072 but it is about the same size and has no problem starting even after weeks without being used. I do top it up occasionally with the trickle charger though.

Whether you want the extra capacity on a boat as a get-you-home safety net if the alternator packs up, now that is another matter. I think I'll be fitting a 110AH Td5 Discovery battery when mine needs changing, just for that reason. I would imagine that is why a bigger one is recommended?

[codprawn]

No I think a bigger one is advised as after a few years batteries lose quite a bit of capacity. I reckon a brand new 60AH is prob better than a knackered 210AH!!!

[Chris]

Bruce,

If you dont mind spending a few quid then a couple of Merlin Odyssey PC1200 totally sealed AGM batteries are very good and a total fit and forget item especially when combined with one of their VSR Relays for split charging . They come with a 5 year warranty.

I had them in my last rib and never had any issues. I will also be fitting them to the new one.

[Justribing]

Bruce

[Justribing]

Bruce

If it helps at all i can start my suzuki140 with a 65amp lesuire battery and it does fine. Once started the engine does the rest of your systems and i dont think you will be drawing more than the charge being put back into your battery. I do now have a 100amp battery running my engine but dont think you need to have two large batteries. If you are wise enough to have a back up system i think you are wise enough to replace it when one goes, a small battery would start your engine and get you home after all its a back up!

Just a thought.

[BruceB]

I ended up getting two Lucas Leisure batteries at 85AH and 600CCA. Should be more than large enough capacity and not too large physically.

[Justribing]

Think you have made a good choice best of luck

[BogMonster]

Originally Posted by Justribing

Once started the engine does the rest of your systems and i dont think you will be drawing more than the charge being put back into your battery.

If you are it will not be long before you are in the poo electrically anyway - a large battery will just last a bit longer before it goes flat

[Justribing]

Your right there !