A question phrased like this has no answer, but we get it all the time. It is the same as asking "How many days can you drive this car before you need to pump petrol?" It could be every 2 days for you, every week for another, and every month for a 3rd driver, even though all could be using the same car.
A more meaningful measure used by most major manufacturers is to state travelling range in kilometres (km) or miles.
You may walk from your house to the nearest market or drive past it everyday, but still be unable to gauge the distance accurately (to the right order of magnitude). Here are some simple methods we have developed through our field experience:
a) By Walking Speed.
The average human adult walks at a speed of 4 to 5 km/h. So if you know how long it takes for you to walk from point A to point B, you can roughly gauge the distance.
For illustration, I'll just assume everyone walks at 4 km/h. So if the nearest MRT is 15 mins walk away, the distance should roughly be:
If you need this for your work, then you would have to imagine how many hours a day you need to spend walking each day (getting to work, moving around in the office, going out for lunch, going home etc.), then multiply accordingly.
b) By Bus Stops
In Singapore, bus stops are typically spaced 500 metres (m) to 600 m apart. So if you know the market is 4 bus stops away, you can guestimate the distance to be 4 x 500 = 2,000 m, or 2 km.
You can also counter check this against walking time, as 2 km should translate to a 30-minute walk or less. However, if the 2 measurements are vastly different, it is better to trust the "walking" method, as it is more accurate.
(c) By Maps or GPS
Obviously! Maps are the best. GPS units are rather inaccurate, and you need to physically walk the distance to find out. So do this only if you have time.
Maps on smartphones are a great way to estimate distance, because they are able to give you routing information between 2 locations, including the distance.
If such technology is not available to you, the previous 2 methods should be helpful.
How much travelling range is good enough?
At Falcon Mobility, as a rule of thumb, we use a factor of 3x. That means, we estimate the distance from your home to the place you usually need to go, then multiply by 3.
A factor of 2 is obvious, because besides getting from your house to the place you need to go, you also need battery power for the round trip back home. Add to that a 50% buffer, and you get a factor of 3 (2 x 150% = 3).
Adding a buffer is important for the following reasons:
- After getting to your destination, you still need battery power to run your errands, such as buying groceries or moving around in the office.
- Batteries wear out over time, leading to reduced range. Without a buffer, the range may be enough for you when the batteries are brand new, but you may end up having to change them every 6 months.
- Going up slope and driving on uneven terrain consumes more battery power. Travelling range stated by manufacturers typically applies only to flat, hard ground.
- The route used by a mobility scooter is longer than that used by someone who walks. That is because people who walk can more or less travel in a straight line as they can step across kerbs or walk up staircases. That is not possible for a mobility scooter because they can only use wheelchair ramps.
- Make an estimation of the distance between your home and destination.
- Multiply that distance by 2 to factor for the round trip.
- Add another 50% buffer. If necessary, increase the buffer if you know you are heavy and/or the route you use has a lot of uphill slopes and/or uneven ground.