BAttery questions

[jellied]

I've got a small issue with a re-chargebale battery for a garden strimmer. I'm pretty sure it's the battery rather than the charger itself but the LED only flashes for a few minutes before indicating a full charge.

The battery says it 18V 1.8Am, a quick search on ebay reveals there is only one bloke selling an exact version of it - the rest are all 2.5am.

would the new high amp version work OK in the strimmer?

[andrew_s]

The question is whether it will fit in the strimmer. If it does, it should be OK.

The jump in capacity is quite likely to be due to the battery changing from NiCd to NiMh. The two are compatible in chargers as well as use. The difference is the higher capacity of NiMh, and that it loses it's charge a bit quicker when not being used.

[Gattopardo]

Can you open up the old battery pack, is it screwed together?

If so you maybe able to purchase the battery pack to replace the one thats in the case as they are usually aa batteries conectted in to a pack.

[rafletcher]

they are usually aa batteries conectted in to a pack.

In a garden strimmer?? I don't think so.

To answer OP, I concur with andrew_s, if it fits it'll be fine.

[Gattopardo]

they are usually aa batteries conectted in to a pack.

In a garden strimmer?? I don't think so.

To answer OP, I concur with andrew_s, if it fits it'll be fine.

Have you taken a battery pack apart?  I've not taken a lithium ion one apart yet so have no idea of those, the Ni Cd and Ni Hyd ones seem to contain AA bateries sealed together and the terminal soldered.

[TimO]

Have you taken a battery pack apart?  I've not taken a lithium ion one apart yet so have no idea of those, the Ni Cd and Ni Hyd ones seem to contain AA bateries sealed together and the terminal soldered.

Whilst some battery packs appear to be composed of AA type cells, often the dimensions differ significantly.  A Li-Ion battery will definitely not be composed of any sort of AA cell, since the basic chemistry differences mean that Li-Ion cells function at around 3v, compared to the 1.5v (more or less) of most other common cell types (ie Alkaline, Zinc Carbon, NiCd, NiMH etc).

[Gattopardo]

Have you taken a battery pack apart?  I've not taken a lithium ion one apart yet so have no idea of those, the Ni Cd and Ni Hyd ones seem to contain AA bateries sealed together and the terminal soldered.

Whilst some battery packs appear to be composed of AA type cells, often the dimensions differ significantly.  A Li-Ion battery will definitely not be composed of any sort of AA cell, since the basic chemistry differences mean that Li-Ion cells function at around 3v, compared to the 1.5v (more or less) of most other common cell types (ie Alkaline, Zinc Carbon, NiCd, NiMH etc).

I've taken apart a B&Q brand battery pack (12v) and found them to be just that,  also a 18v battery pack from screwfix.  Have done two 9.6v bosch ones and found them to be AA size.

Actually do you know why you can get high output AA but as the size gets bigger C or D the output doesn't raise as much as the physical size?

[Wombat]

Rather more likely to be sub C's for a thing like that.  Thats the size that are used to make up model car racing battery packs.  Getting inside the battery pack, and replacing the original cellls with new ones isn't too tricky usually.  just don't try replacing anything else with Li-ion ones, as they are based on 3.7v per cell, and the charging technology is very different.  They are tricky sods and blowing up is not unknown. 

[andrew_s]

Whilst some battery packs appear to be composed of AA type cells, often the dimensions differ significantly.  A Li-Ion battery will definitely not be composed of any sort of AA cell, since the basic chemistry differences mean that Li-Ion cells function at around 3v, compared to the 1.5v (more or less) of most other common cell types (ie Alkaline, Zinc Carbon, NiCd, NiMH etc).

Li-ion cells the same size as AA do exist, and so could potentially be used in battery packs.
They will generally be known as 14500 cells (14mm dia 50mm long), and you can buy them from Hong Kong if you have something that will stand the extra voltage.

[frankly frankie]

Actually do you know why you can get high output AA but as the size gets bigger C or D the output doesn't raise as much as the physical size?

Economies of scale - AAs are where the action is, far more manufactured and sold than the other sizes, so that's where the development goes.

One way to get high-capacity D cells is to use a 2xAAs-to-D converter, like this
http://www.sourcingmap.com/converter-case-into-battery-cell-holder-p-11606.html?currency=GBP
means you can use 2 2800mAh AAs to make a 5600mAh 'D cell' -
I have also heard of similar converters that hold 3x AAs, so giving up to 8400mAh - but have never actually seen one.

[Wombat]

But I'm pretty sure you can get 9Ah D's so whats the point?  Surely if they incorporate several AA's to increase the Ah rating, they must be in parallel, which is a big no-no for low internal resistance cells such as NiMh's.

[Maladict]

The question is whether it will fit in the strimmer. If it does, it should be OK.

The jump in capacity is quite likely to be due to the battery changing from NiCd to NiMh. The two are compatible in chargers as well as use. The difference is the higher capacity of NiMh, and that it loses it's charge a bit quicker when not being used.

Nickel-metal hydride battery - Wikipedia, the free encyclopedia

A Ni-Cad charger should not be used as an automatic substitute for a NiMH charger.