MK date codes

[desert dweller]

Just picked up some batteries for my mobility scooter from an authorized MK dealer. They were clueless about the dates so before I went, I talked to MK.

They said there would be a sticker with the month and year, or an imprint on the batteries in the format of year/month. The sticker on the box says 6/25 so I accepted them. Then I got home and there's the same sticker on each battery plus an imprint that says 240524BD.

I don't get it. Maybe it's a supply chain issue or tariffs. MK carry premium prices in the US and I expected to get fresh batteries.

The only other 22Ah AGMs or gels in my size are cheap UPG or Mighty Max batteries. I'd have to order them online and the last pair I got were over a year old.

LiFePO4s won't work because I'm not physically able to take the scooter apart to remove them and carry them on a plane.

[desert dweller]

Update: Just talked to MK. They said they don't sell batteries that old and to return them to the dealer. As far as the sticker goes, they said that might've been the distributor.

Talked to the dealer and they said they could order new ones. We'll see. This is the 2nd set of "new" batteries in less than a month that ended up being over a year old.

[Burgerman]

Are you sure they are not used?

[desert dweller]

They look new.

[Burgerman]

So do my shiny clean 1 year old ones but they do not perform like new. And its happened and been proven on here before. Its an easy way to make a lot of profit. Rebox someones used battery as new and just test them and charge them. And a polish. Remember most users do less than a mile a day so they get away with it mostly.

Not saying this is the case here. Just that it happens.

Personally I always CAPACITY TEST and then measure the fully charged internal resistance (impedance) to be sure I am getting fresh new healthy batteries.

[desert dweller]

Thanks. I wouldn't be surprised. I also wonder if maybe for some reason there's a shortage of 22Ah batteries or if they aren't used in that many devices, leading to low production.

If so, maybe that's why my local mobility stores keep trying to sell me 18Ah batteries or High Rate 22Ah which I learned the hard way don't last in deep cycle applications.

[Burgerman]

When designing a battery that fit into a specific fixed volume there are 3 competing things.

Internal resistance.
Ah.
Cycle life.

Increase one, say Ah, and the others must suffer.

So if its low impedance, and great capacity then cycle life must suffer.

If you want a long lifespan (cycles), then either impedance (resistance), or capacity (Ah) must be worse.

Now heres the important thing.
A battery with low impedance will allow you to use more of the rated Ah in a chair. So an 18Ah battery may very well take you FURTHER than a 22Ah battery that is higher impedance. So do not fixate on Ah. Because ACTUAL USABLE Ah depends on the rate you discharge tha battery and the internal resistance/impedance as this also increases the Peukert value at the 2 to 3 hour rate we need.

So in a chair, go for the low internal resistance, and good cycle life. Don worry about Ah.

I might add that in a typical chair, you will only ever get between 35 and 50% of the rated Ah before it stops. The point that it stops is more dependent on internal resistance than Ah.

For e.g in the Grp 24 size, the 73Ah MK gel is 500 to 550 cycles. And low to medium Internal resistance. So Ah suffers in comparison to the 80Ah AGMs. But they take you further. Last longer. I once bought a 100Ah Elecsol GRP 24. It barely moved the chair, had about half the range of the MK...

[desert dweller]

Thanks again. I was wondering if there's more to range than just Ah. Interstate's guy told me that their batteries that I got from the mobility store (!) swelled up and died early because they're High Rate.

He recommended their 18Ah deep cycle batteries (they don't make 22Ah). Spec sheet says 15mΩ internal resistance. The MK 22Ah are lower at 9mΩ but if I can't get a fresh pair I might as well go with the trustworthy guy at Interstate.

[Burgerman]

>>>The MK 22Ah are lower at 9mΩ

Thats better. Internal resistance scales with battery size of course too. So a 73Ah GEL MK with 500/550 cycle capability has just 4mOhm. The Odyssey 68Ah has better range, because those are HALF the resistance at 2.5mOhm and 1 inch shorter (Grp 34 is same as 24 but shorter by 1 inch). So I use those. Downside? They have less cycle life, at 400 to 450. But they work better and charge faster.

Its all a compromise. But greater than 9mOhm on a small battery would worry me!

Mk AGMs are low quality, even by MKs own blurb... I wouldnt use them. But that applies to almost all cheap AGMs with only Odyssey being different.

MKs own info:

But in a hot place whatever battery you buy wont last.

[desert dweller]

The "new" MKs measure 11.97 and 12 volts. Is that a problem? I haven't installed them or charged them.

[Burgerman]

Not bad but you should connect them pos to pos, neg to neg, and leave them 16 hours or so.

[desert dweller]

What will that tell me?

[desert dweller]

Does the voltage indicate how old the batteries are?

[Burgerman]

No.
I used to sell batteries. I kept any that were in stock at 13.35v. All connected to a single power supply via jump leads. Sometimes several pallets of them.

Not everyone bothers. They will measure them periodically, and just charge them if below some arbitrary point. Often they only do it before shipping. So nobody knows...

[Burgerman]

What will that tell me?

Nothing. But if you take two new batteries and install them with different state of charge or voltage then one battery will be overcharged and the other will be undercharged the next few times you charge them. This causes the overcharged one to be damaged due to gassing and plate corrosion. And the undercharged one to be sulfated which reduces capacity riht from the start! Yours are close anyway, but sill its good practice to connect in parallel and allow a day to be sure both are identical.

In the end they would both end up equal ayway, as the full one cant get more full... And the other one will then catch up. Depending on how different they were that can take monhs of normal use. At which point both are damaged. This happens all the time! Techs dont check or do this as they dont know, care. or have time.

[desert dweller]

Thanks, that's very helpful as usual.

[desert dweller]

What's the minimum/maximum wire gauge and maximum length? Thanks!

[Burgerman]

For what? Charging?
The charger details are what matters here.

I use a couple of ZXD chargers, for all my lead batteries. It charges a 12A for anything connected via the XLR connector. And up to 50A for anything connected by an Anderson 50 connector.
I use one too for all my lithium batteries via the old PL8 hobby chargers @ 40A.

That is a pre converted power supply that can go from 0-50A and 0-70V and it can also be set to lead as a 3 stage USER CONFIGURABLE charger. That a 3KW capable charger.

See here for real details: Or quik pic below.
https://www.wheelchairdriver.com/board/ ... start=1920

Why? Because all mobility chargers are junk. If I was only doing your tiny battery in a desert then I wouldnt bother with this. Its overkill.

So what sized wire? That depends on the charger.

[desert dweller]

Perhaps I misunderstood. I used some very thin wires with alligators on each end to connect pos to pos and neg to neg and kept checking them but they didn't even get warm. After an hour, they were both 12.5 so I disconnected them and installed them in the battery box.

The weird thing is while they were charging, I could hear a very faint sound from the batteries, almost like a very faint hissing or maybe a very faint bubbling. It was still happening after an hour so I disconnected the crappy mobility charger. The sound stopped after a minute or two and they both tested 13.3V.

My crappy charger puts out 29.4V/2A then floats at 27.4V/.5A. Without temperature compensation, this is within the battery specs for the first stage and .2V over the max float voltage. The air conditioner is blowing on the battery box. I guess I need a new charger but I can't afford the ZXD.

Is this normal? The battery box is up on a table. In the past I've always charged the batteries in the scooter so it's possible this has happened before and I just didn't hear it.

[desert dweller]

ps I have an old Variac. If that would be helpful I'll see if it works.

[desert dweller]

Now they're both 12.6.

[desert dweller]

Definitely a very faint bubbling sound.

[Burgerman]

What has?

Dont connect that! Its AC.

It will boil the electrolyte, charge and discharge 50/60 times a second and wear out and heat up the battery and will not charge at all.

[desert dweller]

Oops, won't try that.

Very faint bubbling sound while the charger's plugged in.

[desert dweller]

Coming from both batteries.

[Burgerman]

Thats gassing.
All lead batteries do that either:
When full.
When charged above a safe float voltage (and when full)
If battey is sulfated or old.

Are these AGMs? If so they may bubble very sightly. The gasses are hydrogen and oxygen. You are splitting water. The battery is recombinent and "recombines" these back to water itself at very low currents.

So either your charge voltage is too high for the temperature or the batteries are knackered, or they are really wet batteries, or your ears are a lot better than mine.

[desert dweller]

I left it off the charger overnight. They're Interstate-branded AGM from Malaysia. 6 months old, 12.6V. It wasn't in float mode according to the charger lights.

Hopefully they're not sulfated. Maybe I'm hearing it because the battery box is up on a table instead of in the scooter.

Thanks for your help!

[Burgerman]

12.6V is about 85% charged though for AGM. After a 2 hour wait with no charging or discharging. You chair when OFF is still dragging down the volts at a few mA.

They should, if not connected to anything sit around 13 to 13.1V when 101% full. After a 24 hour wait to let the surface charge disappear.

After a week, disconnected about 12.95V to 13v. Where they will stay for a month at least. Anything from 12.9 to 13V is as near as matters full as long as they have not been charged or discharged AT ALL for a day. Or more.

[desert dweller]

Yesterday it was 28C. I turned the AC down to 24C today, plugged in the charger, and there's no sound. Doh! Some times I have to learn the hard way.

Once I have the time and money, I'll look into a charger with temperature compensation like the ZXD.

Thanks again for all of your help. I really appreciate it.

[Burgerman]

ZXD doesent have temp compensation. I just look at the day, the weather, he usage, the time I have to charge, the room temp and choose a suitable voltage.