OK, so as you read before, I found a cool Chinese battery. It has a built-in display, a USB port, 3 controllable output switches, a bunch of useful cables and an input for a solar panel! It is marketed as an OUTDO OT100-12. Here is what it looks like again:
The big deal of this battery is that it includes a solar charge controller, which means you hook the solar panel directly to the battery. The function of a charge controller is to extract usable power from the solar panel and charge the battery without damaging it. Who would better know how to charge the battery than its manfacturer?. But what kind of solar panel can you connect? Well, I mailed their support at firstname.lastname@example.org and got a reply as follows:
Dear stefan 1.with controller. 2.maximus voltage 18v Thanks Teana
I think she meant any low-voltage (36-cell) panel. So I connected an older low voltage 40W panel to the charge port and it started charging as advertised. At least I think so, because it has a green LED that started flashing. Yay!
How do you connect other things to it? Well, it comes with a range of nice connectors and cables (look at the pic above, it shows the included cables). The first connector, which I already used, is for the solar panel. It comes fitted with a 2 lever Wago connector that can accommodate up to 4mm2 wire (that's quite thick, in case you don't know :-). The other 3 wires have a round connector on one end, and a 2-wire easy-to-use push-down connector on the other. The battery has 3 "ports" into which the round end of the wires can connect. Each of these ports has an on-off switch and a little red LED to show you whether it is on or off. They are marked with symbols to suggest what each port is for. Two of them are meant for lightbulbs, and the other for a light, fan or TV. There is also a 5V USB port for charging mobile devices. Of course, you can also connect anything else that you may want to the standard threaded battery terminals. Despite all the goodies, well it is still a normal battery.
So how do I use this? Well, it's hooked up to a normal beside lamp with a B22 (standard bayonet) light socket. I replaced the 220V bulb with a 12V LED bulb rated at 7 Watt. Then I removed the 220V wall plug and connected the lamp to one of the round plug wires described earlier. Plugging this into the battery port, yes, it lights up. The colour of the bulbs is a little cold, but that's probably because I did not pay attention whether they were "warm white" or "cold white" when I bought them. Incidentally, you are not going to find standard E26/E27 or B22 12V lightbulbs at your local Pick 'n Pay - I searched for "12V lightbulb" on Bid or Buy to find these.
What are the costs? The battery lists for US$70 in China, but it cost me approximately R2,800 (3 times the US$ price!) at Battery Experts in Durban. Maybe with VAT, shipping (it weighs 30kg) and import duties (no idea), this is normal?. A suitable solar panel for this would be a 36 cell 50W to 120W panel. Such panels should cost somwehere between R500 and R1200 (Feb 2019)
How does it perform? Well, here at home we use it with one 7W light, typically powered 2 hours a day and occasional cellphone charging. The solar panel is an older 40W panel, which is mounted on the roof of a nearby shed (around 4m away) that only gets direct sun in the afternoon. From measurements of the battery, it seems as if it works just fine. On most days it seems to recharge almost fully. Even on cloudy days, it manages. Recently, we had 5 successive rainy days. The system continued to work, with the battery not falling below 12.6V. Here is a measurement of battery voltage for the past few days:
Can I recommend this? Well, like most things solar, it's never going to save you money. What it will do is give you emergency lighting for a few hours every evening and keep your cellphone charged, even if Eskom shuts down indefinitely. There are cheaper ways that this can be done, but not much cheaper. If simplicity and large capacity appeal to you, then this is pretty cool.