Hi all I have this older bike lights that I been using for a few years now.

Yes I think put them as online as chinese but were cheaper, but worked really well dispute being bulky etc.

However the batteries now don’t really hold a charge well anymore, and I have tried buying a new setup, only to have a brand new battery not hold charge well any more either.

Reason yes they were cheap, but I like the lights themselves, durable and work well on the trail for sure.

So I was wondering if anyone knows if I could find an aftermarket battery somewhere that be compatible to these lights, I have a pictures of the lights with the types of cables and connectors needed, as well with the battery that is needed suggestions please.

DC 4V-7.2V maybe.

oh really, hmm

Look at the charger of the original battery. if it has a output voltage of 8.2-8.5V, then it is a 7.2V Li-Ion battery (2 cells in series). Even without the information from your charger, i am 95% sure it is a 2S / 7.2V battery. The plug is a DC5521 connector.

any tags on the light that has an "input" voltage & amperage callout?

I smiled at the roll of duct tape in the picture. Reminded me of the Red Green Show and how the gray sticky stuff is apparently used to fix everything up there! <grin>

Apologies in advance. I couldn't help myself!

so the charger says this
inputt 100v-240v ac 50/60hz
output 8.4v 1a

does that make sense

on the cord of the battery of the lights
it says this

awm 2464 vw-1sc. 80c. 300v 22awg

with those numbers what type of batteries would work on this

would need to math together cells that sum to: 8.4v 1a

Based on what Polyphrast said above, you need two Lithium Ion batteries in series.

Several years ago I bought a similar light, but mine was powered by a USB-A plug. Thus, I can plug it into a powerbank. The really small powerbanks do not have the amperage I need for the light, so I need to upsize it slightly. If you buy a new light, you might consider that option.

I had two versions of that light. You can buy replacement batteries on eBay or Amazon but I would suggest buying an empty battery case that uses four 18650 batteries so you can use batteries of known quality. I took apart the "four cell" battery pack that came with one of the two lights only to find that two of the four cells were just dummy batteries. Example of empty case https://www.ebay.com/itm/315793683962

Electrics in not my superpower, but if I recall, whether it was a battery charger or alternator on a car, the charging output voltage is always slightly higher than the battery voltage. Alternators for 12VDC I think charge at about 14V and if the battery is fresh it actually checks at about 13.5VDC IIRC. So for 8.4VDC charging, I think the battery nominal rated voltage will be less. So 7.2VDC sounds about right. Not 8.4.

The size batteries you need, in Amp-Hours (Ah), depends on the current draw of the light (Amps) and how long you want it to burn before needing a recharge.