Batteries? send help!
 

Hey peeps,
I can't post links so I've tried to include the relevant info below.
I'm still reasonably uneducated on the technical stuff regarding RC electronics.
Hobbyking are opening up their AU warehouse, which hopefully means cheap LiPos but I don't understand :-s
Hobbyking are offering a Turnigy Rapid 6500mAH 140c Lipo for $40
EZPower have a 6800mah for $149
Surely there must be a reason the ezpower is more expensive? but from what I can see on face value the Turnigy battery comes out on top?

• Turnigy:
• ROAR approved
• Precision-matched cells
• Low internal resistance
• Longer cycle life
• Turnigy quality
• High energy density (lightweight and high capacity)
• capable of up to 140C discharge rate

Specs:
Capacity: 6500mAh
Configuration: 2S2P / 7.4V / 2Cell
Constant Discharge: Up to 140C
Pack Weight: 308g
Pack Size: 139 x 47 x 26mm
Balance Connector: JST-XH
Discharge Cable: 10AWG

EZpower:

Features

• 7.6V (HV) Graphene
• 6800mAh
• 70C / 140C rating
• Low Center of Gravity
• 5mm connectors
• 285grams
• 22.5mm height
• EFRA, BRCA and IFMAR approved

Ready for some school? Take a seat :lol:

first off the 7.6 hv just means these are better quality battery cells that can handle the higher volts. The graphene is arguably better at lowering IR (internal resistance - think of battery losses before even leaving the battery). Also the capacity of a hv 7.6 battery needs to be higher IF you are charging at 7.4v. The 6800 is 6800 at 7.6 but if your racing where there’s 7.4 battery limits, your 6800 just became a ~6200mah because it’s not “fully charged”. The plus side to that is less fade. If you look at battery curves, it’s highest at 100% then gradually curves down. If you race stock classes, a flat discharge rate is very nice. You kinda throw away the extreme values on a battery curve. No big drop off from 100-90% and you balance your cars power so you have enough battery to run the race. During the last minute you won’t have to punch the throttle extra to make those bigger jumps if your battery curve is still flatter rather than dropping

staiguy gave you a good explanation why cheap batteries are cheap, and good batteries cost more. The question is, what are you doing with them? If you are "bashing", buy 2 or 3 of the HK batteries and enjoy. If you are new to racing, buy the HK battery until you can complete a main without crashing, then upgrade when you feel you need 10% more performance.

The voltage curve of the HV batteries is nothing special. Lipos drop from peak voltage quickly and then have a curve that's a bit flatter for a longer period. The voltage at that flatter region on HV batteries is the same, they just have a very short period right at the start where it has a bit extra. If you charge the HV to the same starting voltage as the regular packs, you lose that and the curve looks identical.

Not to forget: that EZ Power is 23g lighter and is LCG on top of that.

Fairy tales are always cheaper than the real story. 140C continuous discharge rate?

The other tale actually tells the same. But I think we all agree that today's (actually it's been like this for years) C-ratings are not to be taken all too serious.

The one you quoted shows 2 ratings, 70C continuous 140C burst. But yeah they're mostly all bogus.

No, you're right. Guess I wasn't paying enough attention. Ooops.:eek:

70/140 is actually far more believable than that cheap Turnigy delivering constant 140C.

At first I was wondering why the second battery was so extremely expensive, before it hit me that it's AUD not USD - which made me wonder how cheap and crappy these Turnigys must be then.

Even 70C is not that believable. That's nearly 500A sustained current.

I know, but it's probably the better battery out of these two, and it claims only half as much - so it's going to be much closer (even while probably not close at all) to the truth. :lol:

A little less debatable but more important is c charge rate. Most cheaper cells say 1c, which is the healthiest, or nondestructive way to charge your battery. Others may say 2c, 3c or 10c. These are specs a healthy battery can get charged at and the manufacturer is less likely to get sued :P. Pros need that low ir and do 30 amps up, 30 amps down to prep and heat up their battery before races. This will shorten your battery life. If it’s a cheap battery might not live for long at those rates. At a pro level, a new battery once a month is normal because it loses its competitive edge. Still probably has some good life left in it, if charged at the recommended rating but not for their needs

High charge rates are banned in many areas, and the true pros run mod where IR doesn't matter that much.

Sometimes they do not even fully charge their batteries in Mod (e.g. only charge to let's say 8.30V instead of 8.40V) to take away the extra punch stock racers crave.

Funny thing is that in the US the idea of high current charging has taken a huge role while here in Europe we have people winning the larger races with no more than 2C charging. And as we know the discharge C rating is more like a fiction how well can we rely on the charge specs? The 1C is just a safe rating but does not mean 2 or 3C can not be done but 10C ????? Nope, not my idea to try it.