CHAPTER 7 ■ NINE-VOLT BATTERIESWhen you remove either probe from either battery snap terminal, the meter will display zero again. It’s
worth noting that, in all cases, both probes must be touching the part in order to measure it.
9 V Battery Characteristics
Depending on their chemical makeup and age, the voltage and other attributes of a 9 V battery can differ
considerably (see Table 7-1).
Figure 7-7. A positive number indicates a proper measurement
Table 7-1. Typical Characteristics of 9 V Batteries
Chemical Type Fresh Rated Halfway Discharged Mass Capacity Price
Super Heavy-Duty 9.8 V 9 V 6.5 V 4.8 V 37 g 400 mAh $1.50
Lithium 9.7 V 9 V 8.1 V 5.4 V 35 g 1200 mAh $7.00
Lithium Polymer
(Rechargeable)
8.4 V 8.4 V 7.4 V 6.5 V 28 g 500 mAh $15.00Alkaline 9.5 V 9 V 7.4 V 4.8 V 45 g 595 mAh $3.00
NiMH 8.4 (Rechargeable) 9.6 V 8.4 V 7.5 V 7.0 V 40 g 250 mAh $6.00
NiMH 9.6 (Rechargeable) 11.2 V 9.6 V 8.6 V 8.0 V 45 g 230 mAh $8.00
It may now occur to you that it’s a bit of a misnomer to call the battery size “nine volt” since the actual
voltage varies quite a bit from nine. Somehow the name for the size got mixed up with the voltage. Other
consumer batteries avoid this problem with names like “AA,” “C,” “D,” and so on.
The Fresh column in Table 7-1 is approximately the voltage you may find when you test a brand-new (or
newly recharged) battery not connected to a circuit. Voltage always reads a bit lower when testing a battery
attached to other electronic parts. A fresh battery settles down to the officially rated voltage with age or after
a short amount of use.
The Rated column describes the official voltage the manufacturer claims for this size of the battery. In all
cases except rechargeables, the manufacturers state the batteries are designed to provide approximately 9 V.
The Halfway column was generated by taking the total number of hours the battery lasted until the
discharged voltage was reached, and then looking at the voltage at half that time. This gives a sense of the
voltage when half of the battery capacity has been used up.
In the Discharged column, the manufacturer arbitrarily picks this voltage number. For example, it isn’t
as though an alkaline 9 V battery suddenly stops working below 4.8 volts. However, at some point you need
to call the battery “dead.” By the way, some sneaky manufacturers may claim a battery is longer lasting just
by choosing a lower final acceptable voltage.