# What's a reasonable difference in resistance between batteries in parallel?

I know that the differences in resistance between batteries in a circuit will create different drop, and as a result draw unequally. Unfortunately, I couldn't get my hands on a parallel D-cell battery holder, so I soldered one myself. On my multimeter, I measured as much as a 0.1-0.3 ohm difference between the contacts and ends of the leads, which was more than I was expecting.

I'm using these batteries: http://www.xenoenergy.com/eng/prod/genaral06.asp , and they will be deployed outside in sealed boxes for quite some time.

My question is this: how much of a resistance difference between leads on cells is 'too much' and could yield either catastrophic battery failure or meaningful decrease in battery life?

• The internal resistance increases as the batteries discharge, so the situation is self balancing to some extent i.e. the batteries with the lowest internal resistance will discharge fastest so their internal resistance will rise fastest. – John Rennie Oct 30 '17 at 7:40
• Would Electrical Engineering be a better home for this question? – Qmechanic Oct 30 '17 at 9:15
• Would the internal resistance compensate for the differences in resistance on the battery terminals? And, perhaps it would be better suited to EE. – osteichthyes Oct 30 '17 at 10:08

The 30mA and 100mA curves have a voltage difference of about 210mV, showing an internal resistance of about $3\Omega$. This will dominate your $300m\Omega$ contact resistance, which you can probably ignore. Of course, lower contact resistance is always better.