Adding a second battery
The International Tandem Rally this year (2022) is the first week in August, near Tecklenburg, South West of Osnabrück in Germany. We thought it would be good to ride from home, using the Stena Line Ferry from Harwich to the Hook of Holland. Once in the Netherlands the going would be mostly flat but between us and Harwich and in Germany there would be a fair amount of climbing.
The 17.5Ah battery currently fitted to the Pino is good for at least 40 miles with reasonable use on the unloaded tandem, but I was a bit anxious that hauling the loaded bike and trailer would reduce the range as the motor would be needed more, especially in hilly terrain. With this in mind I looked at either obtaining a second ‘reserve’ battery or another to add to the bike.
The type of connector in the mounting bracket on the current 36 volt 17.5Ah (630Wh) battery, now 3 years old, which I bought from China has been changed and I thought it unlikely to be able to buy a second identical ‘spare’ to match the existing bracket, so I looked at connecting a second battery.
The logical choice was a rack mounted battery. I wanted a system that would allow me to use just one or both. Two batteries for a shortish local ride would be overkill and unnecessary weight. However, on a longer ride, in much hillier terrain or on a fully loaded tour, the ability to have both batteries providing power would drastically increase our range. An advantage to using both batteries at the same time rather than one then the other, is that at maximum draw by the motor, each battery is only providing 50% of the power, so the batteries are not stressed nearly as much as a single battery providing all the power.
Looking for more information on the web, I came across ‘Area 13 e-bikes‘ and some useful videos on battery care and how to add a second battery to an e-bike. With the advice from this video I ordered the Dual Battery Parallel Connector. This would allow me to safely use the two 36 volt batteries of different capacity on the same system, or either battery individually. Something similar is available in the UK, but costs a lot more. Delivery from the ‘States took a little over a week. I ordered some XT90 connectors to match the ones on the Dual Battery Parallel Connector. Because the original battery did not have an isolating switch, I also bought an inline on/off switch so I could isolate the exposed connector on the down-tube battery bracket when we were using the bike without that battery fitted. Without the switch I am pretty sure the connector would be live and very prone to shorting out if it got wet.
The beauty of this system is that either both batteries or just one can be used, without the other being on the bike. The large capacity rack mount battery weighs 5.8kg (12.7lb) and the down-tube battery weighs 3.5kg (7.7lb).