GS750 - which battery?

[ESEN]

Hi all

I need to replace the battery in my 77 gs750 (bored out to 850 pistons) and I need it to be smaller than oem as it goes under the rear seat hump.

Can you tell me if a ytz10s yuasa will be strong enough?

Capacity Ah (20-HR): 9.1
CCA @ -18C: 190

Size wise it's what I need without going crazy on an expensive lithium ion from antigravity etc, but no point if it wont be able to get the old girl going..

Also It often sits for months at a time without being used. Is it best to keep the trickle charger on all the time or remove the battery and keep it indoors?

Thanks all
Steve

[cowboyup3371]

I can’t say anything about the battery but if it will be sitting that long you don’t want it to stay attached to a trickle charger all the time. Doing so will actually drain the battery faster than if you put it on for about 8 hours once a month.

[Rob S.]

Also It often sits for months at a time without being used.

Unless your garage is heated, I'd bring the battery indoors and run the charger for a few hours each week. Ideally, the entire motorcycle should be indoors.

[ESEN]

Thanks both

Not sure I'd get away with bringing the bike indoors though!

No one able to help with the battery spec query?

Cheers

[Gorminrider]

gee, I dunno. Maybe ...but at a guess, If your bike starts easy, it should- but you can help by disconnecting the headlight when you start (maybe add a switch in line with the headlamp ground wire)...saves a little juice-some Newer bikes do this automatically so it's not me making it up.
You might just ask if you can return it if it doesn't work, but not many will want to accept a return when you buy a battery they know is too small for the application.

Your lights and all should run fine when the bike is running and charging. Still, the battery may not last as long as the original.
I have it that the original was 14AH your new is 8.6 AH (190CCA) from my catalogue.

[ESEN]

My bike does start pretty well. I have been using a ttz14s varta battery for the last 7 years on it.

That is 11ah 230 CCA so already lower spec than oem. Maybe I'm pushing my luck too far going for the ytz10s

[Gorminrider]

Well, I'm curious so do report back. The question comes up occasionally, but they don't follow up with results.

Some bikes don't have an "advanced-type " equivalent to the original wet-cell so I've used slightly smaller "agm" without any notable effect, but your ytz10s is pretty close to half-sized..."advanced type" or not. The rate of charge recouping from a hard start would make me careful with "advanced" (or any) battery that is much smaller than the original...

[ESEN]

Thanks. I dont think I have enough info to be confident of spending £80 on a battery that might not be up to the job. I'll keep researching first, but if I do fo for it, I'll report back.

The thing I keep coming back to is that this battery is for 1000cc honda sports bikes, so surely it must be ok for my old 750.. maybe theres more to it than that though...

[Gorminrider]

Esen, I didn't think of it before, but a reasonable comparison might be with an OLD battery of the correct size...I have an old battery I was using over the summer on a 400 that only charges up to 1/2 capacity. It worked ok, but I didn't have many chances if the bike didn't start right away, or I'd left an accessory on when stopped for too long... And in colder weather, one or two spins if the headlight is off. It helps the battery to pause between start attempts,imo.

There are charts online to guess state-of-charge from the resting voltage. You must read up on what "resting-voltage is but roughly speaking, 12.25-12.3V should be close for you. Or a hydrometer of course. And,discharging any starting-type battery demands immediate replenishment or you'll age them, so be careful to do that if you're experimenting with a decent one.


This might give you an indication of whether you should continue to puzzle or give it up.

[ESEN]

Ok thanks. I'll see if I can test that way using my old battery.

[salty_monk]

Why do you need the smaller battery? Custom work?
If so why not fit a decent RR like the SH775 if you haven't already and go lithium. I have an 18ah (lead acid equivalent) battery that's 270 CCA for about a 3rd of the size of a stock one & about a fifth of the weight....

[ESEN]

Hi, Salty Monk, yes it's due to limited space under the rear hump.

The main reason I haven't bought a lithium so far is cost. A good lithium ion battery such as Antigravity costs over £200, and another £100 for a good reg/rec. Plus another £50 or so on a suitable charger.

My current reg/rec is an sh232 and I have no idea if that's up to the job or how old it is.

I've also read lots of stories about how easy it is to 'kill' a lithium battery through simple things like trying for too long to start the bike if it doesnt fire straight up.

But size and weight wise, I absolutely agree on the benefits.

Which lithium battery do you have?

Thanks
Steve

[xkaes]

I can’t say anything about the battery but if it will be sitting that long you don’t want it to stay attached to a trickle charger all the time. Doing so will actually drain the battery faster than if you put it on for about 8 hours once a month.

Can you provide a brief, layman's explanation for this?

[ESEN]

Nudge for Salty Monk, or anyone else who has a lithium battery, around which one you use and anything you've learnt about them along the way?

Cheers
Steve