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[Nordlys]

I have a Tornado 8.4v 5000maH Nimh Battery pack 2 years old.
Having tried it in my boat today (fully charged) the performance of the boat
was less than impressive, in fact it was, by memory, quite sluggish.
 
How can I tell what condition the battery is in?
 
It charged up quite quickly (in fact I thought too fast?)
Voltage across the terminals was 8.4v + still.
 
Same boat, but with prop shaft greased up ready for new season.
Anyone any ideas?
Thanks.

[inertia]

It's very cold and NiMH cells don't appreciate temperatures of much less than 30 degrees - that's Centigrade. That's the first thing I'd blame.
The only way to check a battery is to discharge it from fully charged while measuring the discharge current and the time it takes to get down to its fully discharged state - in the case of your pack that would be when it drops to 7 volts. The time multiplied by the average current should be the right side of 5AH. Much less and your pack is suspect.
The other thing you might check is the charge current which your charger is putting into the pack. For a 5AH battery it needs to be about 5A for 1.4 hours (or equivalent A x H) from fully discharged. The voltage fully charged should be in the region of 10.0v-10.5v. Also don't forget that NiMH cells will self-discharge quite quickly, so it's best to charge them overnight immediately before you go sailing rather than the Sunday before.
The last comment about grease is also relevant; grease gets more viscous as it gets colder, so dunking it into sub-zero water will not make it slick and slippery as a snake!
Hope this helps.
DM

[Nordlys]

Thanks, very helpful.
Temperature was way down, as it has been for ages.
Both operating temp and grease viscosity could well be my problem, I am
grateful that you have pointed this out as this battery was quite expensive
and I couldn't convince mtself that battery was faulty so soon.
Don't think I can obtain all the values that you have written about in order to calculate
the 5AH though.
I will try a complete discharge next and time the re-charge.
The actual voltage I measured across the terminals just now was 9.6v - is that reasonable?
Many thanks....

[sparkey]

  Sounds about right usually 15% above rated voltage of battery pack fully charged at room temp,hope this of some help,
                                                                                                                                                                                                    Ray. [size=78%]        [/size]

[Nordlys]

Sparkey,
Thats interesting, fully charged (2 hours on charge) the battery now reads 9.97v.
 
So I will assume then that the operating temp was too low today to get a
reasonable performance.
Yes, it has been helpful -at least I feel confident that I don't need
to spend another £30 on a new battery!
Thanks.
I will monitor the battery performance when the warm weather gets here.??