How can you tell how much juice is left in a household battery?

Question

I have a digital multimeter, but at what setting do I test batteries?

Answer 1

A few hours ago, I answered a similar question in the Engineering forum. I'll edit that comment for your question:

The discharge curve (voltage vs. time) for most types of batteries is nearly flat for most of the discharge cycle, but becomes fairly steep as the battery approaches depletion. This is primarily because the internal resistance of the battery starts to climb.

The problem is that the nearly-flat discharge curve requires an accurate voltage measurement to determine exactly where you are on the curve. Because you actually have a set of curves, each corresponding to a different temperature, it is rather difficult to get a precise indication of the state of charge of the battery by measuring the voltage.

For many years I have used a Volt-Ohm-Meter (VOM) to get a qualitative feel for the condition of alkaline batteries. I set the meter on the 500 mA DC scale and, observing the correct polarity, put the probes across the battery for 1-2 seconds. This puts a near dead short on the battery, such that the current measured is determined primarily by the internal resistance of the battery.

I look for two things. First, I observe how long it takes for the meter to reach peak current. A sluggish movement indicates a weak battery, but a movement that snaps to the peak value indicates a fresh battery. Secondly, I observe the value for the current at the peak. An old, tired battery will have a much lower peak current than a new, fresh battery. You must also allow that different-sized cells have different response characteristics.

I've never used a digital multimeter for this purpose, but I imagine it would be more difficult to evaluate the first criteria, as you can't watch the needle movement. However, you should be able to read the peak current without a problem

As I said, this gives a qualitative indication of the condition of a battery. I've never attempted to calibrate this method. Rather, if the battery appears to be weak based on the criteria I've given, I toss it out.

Answer 2

on the meter look for DC. look on the battery, it'll say how volts it is. For example, if its a 'AA' battery it is 1.5 volts. so set your multi-meter for 5 volts DC. If its a 9 volt battery set your meter to 12 DC