Battery density vs size

Question

I recently purchased 2 x Class 24 Lead Acid replacement batteries for my mobility scooter. the batteries claim they're 130 Ah, but the old ones, same size, were only 75 Ah.

I tried looking at who else makes these 130 Ah batteries, but now wonder how they shoe-horned an extra 30-45 Ah's into the same size format of the old batteries (Class 24).

The new batteries are also "Lead Acid", so I'm wondering if they are using a new chemical formulation for the electrolytes, different lead plates (if even lead?), or are they trying to "sell me a bill of sale"

I understand how AGM batteries can allow deeper discharge than Lead Acid, down to 20% DoC in some cases, but these are NOT AGM batteries.

I admit, they were cheap, and I understand I AM taking a chance on Wal-Mart branded batteries - EverStart Brand I believe.

I half expected to only get 100Ah of usable energy, which gives me almost double the range, but I'm still curious why 130 Ah. And, of course, HOW!

Is there something else going on in these batteries?

Answer 1

If the original batteries were "original equipment", they may have saved money simply by putting a smaller battery in a large case.

I'm not just being cynical: battery and cell capacity (and chemistry) have always been independent of case size.

Other possibilities are that

(a) they may have used a different plate geometry with more surface area and less volume, to get a larger maximum discharge current, and/or

(b) they may have quoted the discharge capacity where used in that specific scooter, rather than the "nominal" discharge capacity under "standard" conditions.

...or (although I think it's less likely) (c), the reverse, the new battery manufacturer may be more-or-less cheating by specifying the battery for "special" conditions for a "special" purpose.

Note that the definition of "flat" for a lead-acid battery is explicitly a function of discharge current. If you are drawing 75 Amp, then when the battery can't do 75 Amp, it's "flat". So you can change the battery capacity description simply by changing the referenced discharge current. Normally we don't pay any attention to this, because we actually use the number only for comparison. Real life we do something like "start a car", and if the battery won't "start a car", it flat, even though the quoted number is measured under different conditions..

The one place it does commonly matter is for cold batteries. A cold battery won't "start your car", but it will after the battery has warmed up. That's because the current capacity of a cold battery is lower, not because the stored energy has changed or is different.