$about lead acid

What about lead acid
On the face of it, Sealed Lead Acid (SLA) batteries of the type used for alarm system battery backup and in computer Uninterruptible Power Supplies (UPSes), to name just a couple of their many applications, look like a good alternative to NiCd. They use much the same basic reaction as a lead-acid car battery, but their jellied electrolyte (they're also referred to as "gel cells") means you can use them in any orientation without suddenly finding yourself covered with sulfuric acid, and they need no maintenance.
Five 4Ah 1.2 volt NiCd cells will cost you more than $70 (Australian dollars) retail with no charger, whereas a 6 volt, 4Ah SLA battery is only $20, plus $30 for an "intelligent" plug-pack charger that'll switch to a gentle trickle mode when the battery's full. It looks like a no-brain decision, doesn't it?
Well, it isn't. The problems with SLA batteries are as follows:
They're darned heavy. SLA weighs roughly twice as much as NiCd for the same capacity. They take up about the same amount of space, but if you're on the road, or just wandering around a party, you'll be acutely aware that the word "lead" in their title is not just there for show.
They've got a smooth discharge curve. NiCds keep their voltage almost steady for almost all of their discharge, whereas SLAs fade away more rapidly, so in some applications you can't use the last 10% or 20% of the battery's capacity because the device being powered thinks its battery is flat. This is not normally a problem with digital cameras, because they're made to work with alkalines, which droop severely under a 1A load even when new.
SLAs don't like going flat. If you run a lead acid battery flat and leave it for several hours, it'll sulfate and you might as well throw it away. Even the deep-cycle traction batteries don't like being flat for too long. SLAs definitely can't be left flat.
Slow charging. 10 hours is about as fast as you can charge a SLA. You can charge even plain, non-fast-charge NiCds in 90 minutes with a good charger; fast charge NiCds can be charged in less than 30 minutes.
If you've already got a pile of camera gear, throwing a couple more kilos of battery in there won't make too much difference, I suppose. But most digital camera users don't have a lot of accessories (because they can't have a lot of accessories - there just aren't that many available for most digital cameras!) and it's a pain to tote around a super-heavy battery.
But they're cheap, all right. If you mostly stay in one place, or you don't mind lugging a really dense battery pack around, SLA could fit the bill. All good electronics stores stock them, so when you go shopping for battery options, pick one up and see how you feel about it. Personally, I and my underdeveloped musculature are sticking with NiCd.
http://bargain-batteries.com