How much power do sat navs require

[G7PSK]

I have a Mio C520 sat nav that has never run on the internal battery as far as the map is concerned, it has got so that I cannot even program in a destination without being plugged in to a power source yet it will show films or play music for hours but turn it to maps and the message battery to low comes up and the whole unit shuts down, if I measure the battery voltage while it is doing this the reading is 3.8 volts with the map on and 4 volts with it off but playing films.
I have ordered a new lithium battery but this has been like it from new (2007)  the battery date code 070901 not sure if this means the battery was made in 2007, or 2001. But for a unit that is called the mio digi walker it certainly is not a portable sat nav, the battery never in the sat nav mode ran the unit for more than 5 minuets enough time to set the destination get out of the house and plug it into the car cradle.
So I was wondering how much power sat nav require and if there is a fault or short in the unit I have.

[rollatorwieltje]

A SIRF3 GPS receiver pulls about 50mA, not really that much. If the battery capacity is still reasonable, something must get insanely hot inside if it really drains the battery within minutes.

[G7PSK]

Cant find anything hot, but just checked the battery voltage while on charge and reads 3.569 pull the plug and the battery reads 3.982 volts so is there something wrong with the charging circuit as I would have thaught that it should read slightly higher on charge than off.
Best thing is probably to do what I have always been tempted to do whilst driving as the voice is so annoying particularly when it tell me I am over the speed limit when I am doing 40 in a 60 zone, sling it out of the window. 

[G7PSK]

I have a Mio C520 sat nav that has never run on the internal battery as far as the map is concerned, it has got so that I cannot even program in a destination without being plugged in to a power source yet it will show films or play music for hours but turn it to maps and the message battery to low comes up and the whole unit shuts down, if I measure the battery voltage while it is doing this the reading is 3.8 volts with the map on and 4 volts with it off but playing films.
I have ordered a new lithium battery but this has been like it from new (2007)  the battery date code 070901 not sure if this means the battery was made in 2007, or 2001. But for a unit that is called the mio digi walker it certainly is not a portable sat nav, the battery never in the sat nav mode ran the unit for more than 5 minuets enough time to set the destination get out of the house and plug it into the car cradle.
So I was wondering how much power sat nav require and if there is a fault or short in the unit I have.

I should have called this what effect does your test meter have, not enough when testing power sources like batteries.. When I use my Avo meter to test the voltage of the battery after its been charged the reading is only 1.8 volts use a dvmm and I get 4.3 volts so the battery is dud with a high internal resistance, the AVO is 1000 ohms per volt .

[Zero999]

A SIRF3 GPS receiver pulls about 50mA, not really that much. If the battery capacity is still reasonable, something must get insanely hot inside if it really drains the battery within minutes.

But what does it do with the data received?

It will require a reasonable amount of processing power to convert it to a 3D map. My guess is, when it displays maps, the processor clock speed increases and uses lots of power.

[G7PSK]

Just a brief update. It is not the battery itself that is dud but the safety circuit board that's on the battery it wont allow more than a few milli amps through so when the GPS is switched on it shuts the unit down. Wont try to repair the board its far to small and a new battery is on its way.