3.6-V primary cells such as the half-AA lithium thionyl chloride battery used for PRAM maintenance and time-keeping in Macs rarely leak, even after declining to voltages such as 0.1 and below. This decline happens when Macs are left in storage for years without a live mains connection. In normal use the battery is 'spared', that is, reverse-biased, behind a diode, by the Mac's PSU so that the battery does not have to supply current. In that state it can achieve a working lifetime almost equivalent to its shelf life of several years before it reaches the advisable chuckaway point of 3.3V in circuit.
In those Macs with a PMU rather than a CUDA switch, pressing the reset button more than once (or letting it 'bounce' when pressed) can deplete the battery within two days instead of several years. When you replace the battery in your iMac, which should be soon—battery replacement, at USD4 from eBay sellers, is one of the most trifling expenses in keeping a Mac—take care when you reset the PMU. One press only, for a second or so, is all that is needed. If you do, by mischance, press more than once you will need to reset the logic board and PMU by removing all power for 10min. or so, and then press the switch once after reconnecting power and battery.
Your iMac without a battery will lose track of time, unless it is set to get time from a server such as Apple's at startup, only if it is switched off between uses, and not if it sleeps between uses. However, system parameters kept in PRAM will not be maintained well, or will be maintained not-at-all, without a functional battery.
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In those Macs with a PMU rather than a CUDA switch, pressing the reset button more than once (or letting it 'bounce' when pressed) can deplete the battery within two days instead of several years. When you replace the battery in your iMac, which should be soon—battery replacement, at USD4 from eBay sellers, is one of the most trifling expenses in keeping a Mac—take care when you reset the PMU. One press only, for a second or so, is all that is needed. If you do, by mischance, press more than once you will need to reset the logic board and PMU by removing all power for 10min. or so, and then press the switch once after reconnecting power and battery.
Your iMac without a battery will lose track of time, unless it is set to get time from a server such as Apple's at startup, only if it is switched off between uses, and not if it sleeps between uses. However, system parameters kept in PRAM will not be maintained well, or will be maintained not-at-all, without a functional battery.
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