I have noticed that when the TIMER and /EN pins are grounded and the /CHRG pulled high through a pullup resistor (2K), the /CHRG pin oscillates at 10ms low and 20ms high.when a battery is absent. Can I depend on this behavior for battery absent detection? The data sheet does not describe this condition, but it is certainly useful if it is not just an anomaly.
Does the LTC4001 have any upper capacity limit, for example a fixed timeout of X hours? If not, I see no problem with your approach.