Step 10: Connecting battery banks in parallel

Picture of Connecting battery banks in parallel

If we connect the positive power leads from both battery banks together at this point we will have connected the two battery banks together in parallel. This would give us 3 volts output with the combined power rating of the two battery banks. But then we would have to be very careful that we don’t mix battery types or batteries that have different charge states. If we were to put fresh batteries in one bank and weak batteries in the other bank then we might get some undesirable results. The fresh batteries would try to charge the weak ones and they could dangerously overheat. We can prevent this by installing appropriate diodes on each positive lead before they are connected together. This will prevent current from flowing out of one battery bank and then into the other but allow current from both battery banks to reach the MintyBoost.

Refer to the first image below. Cut both positive battery leads relatively close to the edge of the battery case as shown. This will help conserve the limited amount of space in the Altoids tin that we’ll be working with after the MintyBoost has been installed.

Next install diodes on the ends of each positive leads keeping the diode leads as short as possible to conserve space. Make sure that the ends of the diodes without the little silver stripe (the anode ends) are connected to the positive battery leads; this is critical. The leads on the end of the diodes with the silver stripe indicate the cathodes and these will be twisted together and connected to the MintyBoost positive input voltage connection.

Make sure these connections are insulated from each other. You can see in the first image below that I used a bit of heat shrink tubing on one lead to accomplish this. Then, as shown in the second image, the entire diode bundle was insulated with more heat shrink tubing.