First of all a pacemaker is a combination of two parts: the generator which contains the battery and logic, as well as the leads which connect to the heart. The batteries are not 'recharged'. When a pacemaker's battery is nearing the end of it's life (roughly 5-8 years) the patient schedules surgery, where the generator but not the leads are completely replaced. This isn't as drastic as it sounds and not usually as complicated as the initial fitting of a pacemaker. This operation is sometimes colloquially called 'recharging' but in reality the entire generator (battery and all) is replaced with a new one while the old is discarded.
It could be that the batteries are getting old and need to be replaced.
because they run out of energy
Generator and the batteries it charges.
It doesn't use batteries, there is a little generator type thing on the front wheel that tells the rear when to shift.
Correct new and used batteries should not be mixed together due to reduced life span and other potential hazards from mixing. Batteries when being replaced should always be replaced with new batteries of the same size and brand if possible.
batteries need to be replaced
The batteries may not be in correctly.
Most of the material is recycled.
Sump pump batteries typically last around 3-5 years before needing to be replaced.
Canon batteries typically last for about 2-3 years before needing to be replaced, depending on usage and charging habits.
If the fan/heater is heating as well as fanning, then the generator can't even support that alone, never mind the batteries. The generator is rated 1,000 watts, and the fan/heater wants 2 KW = 2,000 watts to fan and heat. That's 100% overload on the poor generator. The generator will complain, and the heater will be barely warm.