Garden Light Rechargeable Battery

[Greorge]

I replaced some 600mA NiCad batteries in my garden lights with the same type I got at Burnings.

Right now they seem to be bit weak, suppose winter limited Sunrays don’t charge them much.
I turned switch to off for few days and it seems to have helped a bit for light to stay on longer in the evening.

But since NiCad batteries develop memory I started to think that the next time it will be good idea to put there some NiMh batteries instead.

Would it be OK to put some 1800mAh NiMh low self-discharge batteries or it makes no sense?

[IanB]

It's expensive, but should work fine.

[retiredcaps]

It would be interesting to see how the Panasonic Eneloop Lites would do with a claimed 1000mAh and up to 5,000 charges.

http://en.wikipedia.org/wiki/Eneloop

"Panasonic Eneloop Lite
Along with the upgrade of the regular Eneloops in April 2013, the lite version was also upgraded. It can now be recharged for 5000 times (model numbers BK-3LCC for the AA and BK-4LCC for the AAA battery). The upgraded batteries also retain 90% of the charge after one year like the regular eneloops."

[richard.cs]

Probably not worth it, they're limited by solar input rather than by the batteries so extra capacity doesn't help.  They also get hammered flat every night so no memory. Of course they could just be worn out, in which case put the cheapest rechargables you can find in them

[poot36]

If this solar light runs off 2 aa or aaa batterys you could try moding it with a li-ion or li-polimer battery out of a old mp3 player or cellphone that does not power that device for a usable amount of time.  When I did this I removed the protection circuit so that it would not drain power from the battery or reduce the power going from the solar cell to the battery (Only do this if the solar light has a diode to prevent the battery from dischargeing into the solar cell, if not leave the protection circuit in place!).  My solar light has been going for 4 or so years with a li-polimer battery from a old ipod (gray scale screen and cf microdrive) that I tried to manually recharge and it charged so fast that the cell swelled so that is why it is now in the solar light so that if it decided to vent and catch fire it would only burn the dirt outside.  It has survived -30C winters so I think that it would work very well in your climate just watch out for the slugs!

[PepeK]

I am not sure if this is the right case for a solar based technology. Consider the price of NiCd / NiMH / Li batteries and compare it to the price of electricity if it is mains powered.

[amyk]

If this solar light runs off 2 aa or aaa batterys you could try moding it with a li-ion or li-polimer battery out of a old mp3 player or cellphone that does not power that device for a usable amount of time.  When I did this I removed the protection circuit so that it would not drain power from the battery or reduce the power going from the solar cell to the battery (Only do this if the solar light has a diode to prevent the battery from dischargeing into the solar cell, if not leave the protection circuit in place!).  My solar light has been going for 4 or so years with a li-polimer battery from a old ipod (gray scale screen and cf microdrive) that I tried to manually recharge and it charged so fast that the cell swelled so that is why it is now in the solar light so that if it decided to vent and catch fire it would only burn the dirt outside.  It has survived -30C winters so I think that it would work very well in your climate just watch out for the slugs!

That is an... interesting reuse of lion cells. Usually once they swell they have so little capacity left (due to internal delamination) that they're worthless for powering anything, but I guess solar lights use so little power that it's enough - I've seen ones that use a supercapacitor.

[Greorge]

Thank you all very much for replies.

Noticed that Aldi sells low discharge 4 AA or 4 AAA batteries for $7, so cost per battery is very low.

Have few old Li Ion phone batteries, but one is 2.4V and other one is 3.7V
Not sure it it is good replacement of one 1.2V NiCad battery, also if it will fit inside garden light box anyway.

Will have to check it out.

[poot36]

You can only use the Li-ion or Li-polymer  battery if the solar light has 2 or 3 AA or AAA batteries.  You do not want the Li-ion or Li-polymer to go much below 2.5 Volts or so.  Do not try to use it on a solar light that has only one (1) AA or AAA battery!  You will not fully charge the battery and the higher initial voltage of the battery will damage the solar light!

[Flenser]

Right now they seem to be bit weak

1) Don't judge the garden light performance by what you see in winter.

I did some testing on a solar garden light in January here in Melbourne and at midday under the direct summer sun the charging rate was 26 mA. Today under bright overcast conditions in winter the Sun was behind a white cloud and very bright to look at directly. The garden light is only getting indirect lighting in these conditions and the charging rate was only 2mA.

This particular garden light runs the LED at between 9 and 8 mA so on overcast days in winter the battery is only going to charge up enough to run the LED for a couple of hours each night.

The size of the battery is not going to make any difference to the performance during these overcast days.

[EDIT] 12pm Monday Melbourne is full overcast. The charging current for the same garden light under these conditions was only 6.4uA.

Would it be OK to put some 1800mAh NiMh low self-discharge batteries or it makes no sense?

2) You can test your own garden light to see what you can expect with an AA battery during summer. You may not need to go the trouble of adding Li-ion cells or multiple AA batteries. You may find you will get enough from a single large capacity AA.

I have an Arlec Trillium garden light that uses a single AA battery that I did a different test on. I charged a 1000 mAh battery fully, put it into the garden light, turned it on and put it upside down on a table. This blocks all light to the solar cell so the LED is on 100% of the time.

Date               Battery voltage LED brightness
Wed 01:30am 1.365V              Very bright (uncomfortable to look at directly)
Wed 11:45am 1.301V              Very bright
Wed 09:30pm 1.292V              Very bright
Thur 01:30am 1.290V              Very bright
Thur 09:30am 1.287V              Very bright
Thur 09:30pm 1.286V              Very bright
Fri    03:50pm 1.279V              Very bright
Sat  00:30am  1.272V              Very bright
Sat  01:00pm  1.252V              Bright
Sun 02:11am  0.807V              Dull

I replaced some 600mA NiCad batteries in my garden lights

3) Check the capacity of cheap AA batteries, don't trust the marking. I have some batteries that came with one of the garden lights I have and which are marked 600 mAh but when tested on my charger only take 270 - 330 mAh.

[Greorge]

Don't know how and don't have gear to test true mAh capacity of rechargeable battery.

I turned off couple of garden lights for 3 days and they charged up a bit, but still went dim shortly after sunset.

Might pull the batteries out and charge them on battery charger to see what happens.