Electronics, Lighting, & Gadgets - Assemble aftermarket battery for Cygolite Rover II ?

I bought a CygoLite Rover II. It's on its way now.

Already I'm thinking of getting a bigger battery. The NiMH water bottle battery it comes with is only good for 2 1/2 hrs on high. My max night ride is about that long, maybe longer sometimes. The battery is 4.8 V. Don't know the mAh capacity. The light is a 255 lumen total two LED. I think I read somewhere the battery is about 2500 mAh but I can't find that reference now. Does that square ( 4.8 watts ~= 255 lumens) ? EDIT - In another thread I see 1 watt ~= 40-50 lumens, so this is about right.

Question for the board: Is it OK to assemble a 4 x D cell (~ 10000 mAh) 4.8 V NiMH and just plug it in to the CygoLite? Would this give me about 10 hrs if it's a typical ~250 lumen LED light?

Question II: Does batteryspace.com give good service and sell good stuff? Will the batteries & charger last as expected?

Thanksalot!

-Duffer

Can"t help you with your technical question, but FWIW I have used batteryspace.com and have been very happy with them. I wouldn't recommend you use Alkaline batteries. They don't handle the higher loads very well. In addition when the temperatures start to fall their reliability drops to zero. But if you plan to use a rechargeble D-cell, then I would say go for it. What do you have to lose. Even if it is a miserable failure, you will have learned something. You should see the shoe box I have of my "failures".

Also take a look on ebay. There are several dealers selling water bottle batteries that are Ni Cad, NiMH, and Li Ion that have higher mAh ratings and thus longer run times. Take your pick which kind of battery you want.

Yes, thanks for the recommendation for batteryspace. NiMH cells for sure. Going to get an extra set & also use them in a radio. Wondered whether the batteries were really good for "500 cycles" as claimed, and whether the smart charger was really smart enough not to kill them young.

Specifically, if the 'smart charger' detects negative delta V, has two settings 1 A and 2 A, and recommends changing between 1 A for batteries < 2000 mAh and 2 A for > 2000 mAh... will it have a problem detecting (a slower to change?) -dV for a 10000 mAh pack?

EDIT - OK so I've been inspired to google for answers - here's an interesting site - http://www.powerstream.com/NiMH.htm. Says -dV is not reliable. Says charging efficiency is typically ~66%. (1.5 Ah of charging gets 1.0 Ah of charge). Also says if charging at <= C/10, don't have to worry about overcharging. So I'll get the 600 mA charger ( =C/17 for 10000 mAh D cells ), and charge for over 24 hrs or so w/o worrying about overcharging. Is this OK?

Edit 2 - I got over the fear and cracked open the water bottle battery case. There is a 4/3A x 4 battery pack in there. These are marked '2500 mAh' while at batteryspac*.com the new 4/3As are good for around 4000 mAh. So I'm not sure how many mAhs are actually there, but I'm sure that AAs will work well enough, given that NiMHs are happy giving current at least up to C/1. Connector looks like a 'Mini Tamiya' with female pins male housing. I've ordered two 4xAA holders and two connectors and 12 new NiMH AAs, already have a smart charger for AAs. I'll be ready for a much longer night ride than I can imagine doing.

Edit 3 - It's a nice light. '255 lumens' or whatever, it's more than enough for me. I haven't challenged the battery enough yet to know if it's good for the claimed 3 1/2 hrs.