Topic: cb750a - which battery?

[nixon]

Hi
Searched for awhile but kinda unclear..
Just checking what battery specs your running, either on stock or with LED lights.

The factory seems to be a 21ah monster, is that needed?  YTX 18L

What's the downside to using a 9,12 or 15ah, thebattery will overheat?
Any help appreciated!

[raymond10078]

Some facts:

• The battery capacity (in amp-hours) has nothing to do with electrical load when running.  The stock or LED lights question isn't really relevant.
• The starter rating (power draw/load/torque output/speed/duty cycle) is the same for the A bike as for the 77/78 K and F bikes.
• The batteries for the 77/78 K and F bikes is smaller (14 amp-hours).

In my opinion, the A bike was provided a larger battery for two reasons:

• The starter must also spin up the converter - an inertial/fluid load that the K and F bikes don't have.  This likely contributes to more starter load, which could drop battery voltage when cranking.
• The A bike has a kick starter, but in keeping with trying to sell these bikes to "non bikers", having a good strong battery was likely a good idea.  I have used the kick - it's not fun on this bike.

A fully charged smaller battery will not overheat.  The only way to overheat a battery is to push too much current through it - and that depends on the voltage regulator setting.

Now, if the battery is flat, the A bikes larger alternator may have the capability to push too much current through it, that'd be my only caution.  In my opinion, a K or F 14 amp-hour battery would be fine.  The only risk - if you are a cold weather rider - is that the battery voltage could drop too low and the ignition won't fire - even though the starter is spinning the motor.

As for my bike, I'll be keeping the larger battery.  I do that with my cars, too - I buy high CCA-rated batteries.  I like my starters to spin fast, and my engines to start quickly.

[nixon]

Thanks for your detailed response!

I guess i was thinking after starting,  LEDs will have less drain so will recharge quicker ?


Also, SLA & AGM seems to be a factor, the latter seems to be the best battery for our bikes recharging much quicker , so maybe a 14ah AGM is comparable to the old style 20ah?

[raymond10078]

You are correct that less "system load" will provide more available current/voltage for the battery - to recharge it quicker.  Although, let's assume a starter is engaged for 10 seconds, the battery would be re-charged in a few minutes (or so) of riding, so the net gain to the system/battery, when using LED lights, is slight.

However, if you've upgraded to an LED headlight, the gains will of course be more pronounced.  The charging system will be able to hold a higher voltage at lower revs, and when revved up, will have more power available for charging.

A 77/78 F/K bike AGM should be a good choice.  Here are some Yuasa battery specs for Cold Cranking Amperes (CCA) the various bikes/batteries:

77/78 F/K battery (stock 12N14-3A), CCA = 128 amperes.
77/78 F/K battery (AGM YTX14-BS), CCA = 200 amperes.

76/77/78 A battery (stock Y50-N18L-A), CCA = 260 amperes.
76/77/78 A battery (AGM YTX24HL-BS), CCA = 350 amperes.

You can see that the 77/78 F/K bike AGM battery gets close to the non-AGM rating for a the A bike battery.

FYI:  The amp-hour rating expresses how much capacity is in the battery.  A 20-amp hour battery loosely indicates that a 1 amp load could be drawn for 20 hours before the battery is depleted.  A 14-amp hour battery would last 14 hours for the same draw.  This correlation falls apart for high loads though, so it is just a generalization.  Think of it like the AAA, AA, C and D size batteries.  All are 1.5V, only the capacity differs.

[nixon]

thanks for explaining..i finally get it..

I guess I was trying to gauge the minimum needs to start the A for those 5 seconds with electronic ignition..and maybe save a kilo or 2.

Doesn't seem worth it.

 found a decent line of AGM product called motobatts over here.


2 options that fit, one 25 ah & cca 285, other 21 ah and 310!


I

[raymond10078]

I did say that I thought that a smaller battery would work for you.  A bike in good tune should start easily - and I'm sure that a smaller battery would work, and you could save that weight.  I'm also sure that a battery smaller than the F/K bikes would work too - but if the bike needs extra cranking time - the battery may just go before the bike starts.

In summary, I'm sure smaller will work - but I can't in good faith tell you how small is too small.  The CCA and amp-hours numbers are good guides that can help make that decision.

[nixon]

Appreciate your input.

9 and 12 ah definitely not worth the risk, and they weigh 3kg.

14 ah COULD be ok, and weighs about the same as 21 ah and not much difference $

33
got the 310 cca one.smaller size than stock. Will weigh

[limerence]

kandrtech,

which battery do you have in yours (make and model please)?

[raymond10078]

Yuasa
YTX20HL-BS

[limerence]

Looks as though on the Yuasa website it lists the YTX24HL-BS as the one for the CB750A. Is there a reason why you went with the YTX20HL-BS?

[nixon]

seriously - i'd ditch the old liquid acid yuasa

an AGM battery has more CCA and wont discharge as quick. and no maintenance also

 Just my 10c

[70CB750]

seriously - i'd ditch the old liquid acid yuasa

an AGM battery has more CCA and wont discharge as quick. and no maintenance also

 Just my 10c

+1 

[limerence]

Yep I just ordered the Deka ETX18L battery that is AGM. I was just trying to get an understanding of why choosing one battery over another, and if it was for fitment reasons.

Thanks,
John

[raymond10078]

Looks as though on the Yuasa website it lists the YTX24HL-BS as the one for the CB750A. Is there a reason why you went with the YTX20HL-BS?

Sorry for the delayed reply.

It's been a while since I bought the battery.  I recall that the Yuasa catalog at that time didn't have an AGM battery listed for my bike.  I purchased the battery based on dimensions and terminal locations - and it worked fine. 

[limerence]

Thanks.

I was thinking about doing the same thing, buying by dimension and where the terminals were located. However, I couldn't find a chart of all the Deka batteries and their dimensions so I just went with the batterymart wizard and it choose it for me. From what I have read, Odyssey batteries are very reputable and they also make the Sears Die Hard batteries as well. However, in reading threads about Deka vs Odyssey, many like the Deka batteries more. And for those that buy through BatteryMart, the "Big Crank" is a rebranded Deka.

-John

[nixon]

well. it lasted 5 year. considering i never really maintained it  much, ie not a regular ride and didnt trickle charge, im happy with that. only in last 6 months had to charge a few times.

MBTX20U AGM 21 AH 310CCA ,  it was smaller physically than stock so had to pack it with rubber

Im now gunna grab a stock size  R50N18L-A2  AGM - 450cca 21 AH 7.3kg ..  hope it lasts 5+ this time!