Battery Amps per Hour (Ah)

[brianc]

Hi,
I bought an electric trials bike yesterday for my 4 year old grandson. It was an impulse buy from an auction.

It came with two 9.0Ah 12v batteries, which are wired in series. They are swelled/bloated so I intend to replace them in case they burst, I have seen 12v batteries online with the exact same dimensions but with a much higher Ah rating.

Am I correct in thinking that the higher Ah means they will last longer? I don't want to fry the controller and/or motor

 

[Dibs-h]

Am I correct in thinking that the higher Ah means they will last longer?

That would be my thinking. Along with taking longer to fully charge.

 

[mudman]

I'm not a battery expert but I believe that yes, it means that they will last longer. However, you need to make sure that the replacements can handle the rate of discharge and any peaks. Discharging a battery faster than it's designed for can cause overheating and fires (might be what caused the bloating in the current ones). Also be careful if a different chemistry. I don't think a charger for a lead acid battery can be used on Li-ion ones.

 

[Dibs-h]

I don't think a charger for a lead acid battery can be used on Li-ion ones.

Correct - different charger (types).

 

[ajs]

I would imagine these are some form of lead acid cell given the likely discharge current? If that's the case I would caution that there are several varieties of them. On load to a first approximation it's a difference without a difference, but they have slightly different charging requirements, the final voltage varies. We're only talking a couple of hundred millivolts but it's enough to quickly kill the batteries if you get it wrong.

I'm going to make a blind guess that your existing batteries are either Y9-12 or NP9-12. The number before the hyphen gives the capacity so yes higher there is better assuming they are the same form factor. The number after the hyphen is the voltage, keep that at 12. The letters indicate the specific battery technology, don't change that.

 

[Sideways]

From the look, the originals are lead acid gel batteries possibly made by Yuasa. That's a good brand widely used on real motorcycles to power the engine starter, run the ignition and power the lights.
Like a regular car battery they are not designed for regular deep discharge but the manufacturers of your electic toy probably don't much care. China has millions of electric scooters that are likewise powered by lead acid batteries. In daily use, these lose a large proportion of their capacity inside a year and need replacement every year or two.
In a toy that won't be used all that often, I'd buy the same or similar batteries. Greater Ah is absolutely fine but measure the dimensions to be sure the replacements fit in the bike.
Remember batteries discharge over time and deteriorate if left discharged so charge it after every use and if the toy doesn't get used, charge it up every 2 or 3 months anyway to keep it good.

 

[ChaiLatte]

From the look, the originals are lead acid gel batteries possibly made by Yuasa.

You can zoom in on the photo and read what is actually written on them: 'Master vision' and 'AGM' are visible, as is the China Export mark, so you have the correct chemistry/technology but incorrect quality level.

 

[brianc]

I'm going to make a blind guess that your existing batteries are either Y9-12 or NP9-12. The number before the hyphen gives the capacity so yes higher there is better assuming they are the same form factor. The number after the hyphen is the voltage, keep that at 12. The letters indicate the specific battery technology, don't change that.

Yes, they are sealed lead acid batteries although I have no way of knowing if they are the originals. They are prefixed with "MV" if that makes a difference?

 

[brianc]

I borrowed a fully charged 12v 20ah battery earlier to see if it would spin the motor up but nothing happened, unfortunately. I managed to find an old multimeter and had a quick Google to remind myself what to do with it

Working back from the battery itself I have power after the mainline fuse and into a 4-prong relay before it heads up to the ignition which works fine as power switches on and off as expected. Power then feeds the throttle assembly and potentiometer (restricts max power for new riders) before heading into the controller. My thinking is that either the relay or controller is knackered, or both.

I put power direct to the motor and the rear wheel went from 0 to 100% instantly, it's a good job the tyre was raised off the table or else the whole kaboodle would have taken me out!

Current state of play is, spaghetti junction...

 

[Kittyhawk]

A couple of things I've learned the hard way from living full-time with 12v electrical systems.
Batteries don't just die, they are usually murdered. If batteries are bloated it's due to deep discharging and also overcharging. Its important to match the charger to the battery. I've forgotten now but I think the rule of thumb is that the output of the charger in amps should not exceed 80% the ah rating of the battery being charged.
And most importantly, never discharge a lead acid below 50% of its capacity because it won't fully recover and continuing to do so will hugely shorten its life.
A healthy fully charged 12v battery straight off the charger should read 13.8v and then settle to 13.4v. Your best friend for battery management is a little cheapie 12v voltmeter, and never let it go below 11.9 - 12v. This is the magical 50% capacity mark. Obviously it will drop below that during current draw so it needs to sit for a few minutes under no-load to stabilise and give a true reading as to its status.
Observing the above, my deep cycle batteries were 9 years old with no discernible deterioration when we sold the boat.

 

[ajs]

Actually I've just realised I'm talking crap about the letters. The Y prefix is Yuasa's prefix for the Yucel budget brand. NP9-12, Y9-12, it doesn't make any difference. Some manufacturers do use their own prefixes as you're seeing here but equally others follow Yuasa's naming scheme. They're all AGM batteries which is the important thing.

 

[brianc]

And most importantly, never discharge a lead acid below 50% of its capacity because it won't fully recover and continuing to do so will hugely shorten its life.
A healthy fully charged 12v battery straight off the charger should read 13.8v and then settle to 13.4v. Your best friend for battery management is a little cheapie 12v voltmeter, and never let it go below 11.9 - 12v. This is the magical 50% capacity mark. Obviously it will drop below that during current draw so it needs to sit for a few minutes under no-load to stabilise and give a true reading as to its status.
Observing the above, my deep cycle batteries were 9 years old with no discernible deterioration when we sold the boat.

Thanks for the charging tip, the borrowed 20Ah battery is currently being charged at 10 amps which should be fine

These bikes were supplied with a charger that plugged into a round 3-pin socket on the frame although that is something that's on my shopping list now.

 

[brianc]

Actually I've just realised I'm talking rubbish about the letters. The Y prefix is Yuasa's prefix for the Yucel budget brand. NP9-12, Y9-12, it doesn't make any difference. Some manufacturers do use their own prefixes as you're seeing here but equally others follow Yuasa's naming scheme. They're all AGM batteries which is the important thing.

Ah, that explains the MV prefix then

 

[mudman]

I borrowed a fully charged 12v 20ah battery earlier to see if it would spin the motor up but nothing happened, unfortunately. I managed to find an old multimeter and had a quick Google to remind myself what to do with it

Working back from the battery itself I have power after the mainline fuse and into a 4-prong relay before it heads up to the ignition which works fine as power switches on and off as expected. Power then feeds the throttle assembly and potentiometer (restricts max power for new riders) before heading into the controller. My thinking is that either the relay or controller is knackered, or both.

I put power direct to the motor and the rear wheel went from 0 to 100% instantly, it's a good job the tyre was raised off the table or else the whole kaboodle would have taken me out!

Current state of play is, spaghetti junction...
View attachment 145434

If the original batteries are 12V in series, then this give a total of 24V required so the single 12V probably won't cut the mustard.

 

[Jameshow]

Thanks for the charging tip, the borrowed 20Ah battery is currently being charged at 10 amps which should be fine

These bikes were supplied with a charger that plugged into a round 3-pin socket on the frame although that is something that's on my shopping list now.

Still quite a fast charge better with a 4 amp charger tbh.

 

[sometimewoodworker]

Thanks for the charging tip, the borrowed 20Ah battery is currently being charged at 10 amps which should be fine

that as has been mentioned is a very high charge rate, can the battery accept it? Sure.
Will it chop 50% of the batteries life? Probably, if you use it often.

 

[ChaiLatte]

If the original batteries are 12V in series, then this give a total of 24V required so the single 12V probably won't cut the mustard.

That is a good observation. It goes a long way to explaining why nothing happens when the controller is in circuit (it should sense the voltage and cut out if too low to protect the batteries). It also explains why the motor goes from 0 to actually 50% when the battery is applied directly to it.

For me, the next step would be trying a proper 24v into the controller and seeing if it functions. Then you will know if you have to buy just two new batteries or batteries and controller.

Just a minor technical quibble: it is 'amp hour(s)' not amps per hour.

 

[brianc]

If the original batteries are 12V in series, then this give a total of 24V required so the single 12V probably won't cut the mustard.

Ah ok I will need to borrow/liberate another battery...

 

[brianc]

Still quite a fast charge better with a 4 amp charger tbh.

It's an old car battery charger and has a 3 amp charging option so I will definitely use that next time...

 

[brianc]

that as has been mentioned is a very high charge rate, can the battery accept it? Sure.
Will it chop 50% of the batteries life? Probably, if you use it often.

Thanks, it's a new battery for a ride-on mower which should keep it charged but I'll know for next time